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Scosche TA-03 Wiring Kit Noise Mod

118K views 254 replies 67 participants last post by  2way 
#1 · (Edited)

Left: Original Scosche TA-03 (came w/BlueBox) <------> Middle: Scosche TA-03HB (harness only/no BlueBox) <------> Right: Best Kits BHA8113 identical to orig TA-03 (search eBay)
Note: orig harness (left) doesn't have a shell covering the pins so it's easy to mod, newer harness (middle) has the extended shell covering the pins making it difficult to mod, and BHA8113 harness (right) is identical to the original TA-03 so GET THIS ONE!

20-Pin Toyota Wiring Harness w/RCA for 2K & Up Premium 8-spkr w/FactoryAmp Mod for:

The Scosche TA-03A & TA-03B Harness
and BestKits.com BHA8113 Harness


(update 1/05: This mod fits 2000 & up GT's & GTS's w/optional Premium 3-in-1 AM/FM ETR/Cassette/CD w/8 spkrs & separate amp)
= click to jump to post about which GT's this will fit & about TA-02 harness vrs. TA-03 =


(update 7/07: Latest notes on the new TA-03B Harness, BestKits.com BHA8113 harness, Metra TYTO01 harness)
1) Some time ago the original Scosche TA-03 was superceded by a newer TA-03B harness which uses a different connector that has an extended shell covering the pins, making it more difficult to mod.

2) When selecting resistor values from the Termination Resistor Table for the newer TA-03B, add +16% to the value from the table, or use the following calculator to find the exact value, substituting 2200 ohms for R1 (the TA-03A uses 1900 phms for R1): Voltage Divider Calculator

3) There are many wiring harnesses out there which claim to be compatible with the 00-02 / 03-05 Celica's but members have discovered are not compatible. We know the original TA-03 was the easiest to modify and absolutely works, as well as the newer TA-03B, even though it's a bit more difficult to mod. We also know the BestKits.com BHA8113 Harness also works, and may still have the original Scosche TA-03 style connector that's easier to work with.

4) Recently members have been asking me about a new "compatible" harness called the Metra TYTO01. At this time all I can say is that it looks like it might work with later JBL-equipped vehicles which use the Toyota databus to control Turn-On. Other than that, I don't know yet whether it needs the mod or not. Note: Metra does not list any Celica's in their TYTO01 compatibility table.

(update 8/07: )
1) Confirming: the BestKits.com BHA8113 Harness is identical to the discontinued original TA-03 harness, including long pins making it easy to modify compared with the newer Scosche, so I'd recommend you use the BHA8113 instead of the Scosche TA-03B.

2) If your HU only has two RCA outs (L&R) you can use an RCA Y-Cable to connect to the StockAmp's Rear RCA's, but you'll need to roughly double the value of the termination resistors to avoid double-terminating the signals. For example if the table says use 600 ohms, use 1000-1200 ohms instead.


PacificBlue
--------------------------------------------------------------------------

You might think installing an aftermarket head-unit and hooking it up to the existing FactoryAmp would be a piece of cake, esp. using Scosche's TA-03 wiring harness and matching Toyota connector. Not so, and like just about everyone else here who's tried it I got loads of ECU noise, power-window buzz, dimmer buzz, and the worst: alternator whine. After installing and removing my HU about a dozen times trying things, I was about ready to throw that fancy HU out the window and put the stock unit back in, until...

I love my Celica like most everyone here does, and cuz I got so much help from reading the posts on this board, I'm posting this to give a little back. So I hope I do this right...

I'm an electronics engineer, but after re-checking everything it all looked like it was hooked up ok, aw crap. Like everyone else I thought it must be a grounding problem. Well, yes & no. And what's with the blue box Scosche gives you with the switch on the side? I wasn't about to give up because I know how good the stock GTS Premium Stereo can sound, so that FactoryAmp can't be all that bad... so I kept going.

In a nutshell... I found out our GTS Premium 4-channel FactoryAmp has high-impedance inputs with virtually no input termination. This means when you hookup most head-unit's PreAmp Outs (which have virtually no output termination) the RCA cables and the Celica's own HU-to-FactoryAmp wiring harness act like radio antennas picking up every little electrical noise generated by the car. Have you ever stuck your finger on the end of a guitar cable with the amp cranked up? Same thing.

On top of that, the TA-03 has a 1.9k resistor in series with every RCA cable. If you feel the heatshrink, you can feel the resistor inside each cable.

Solution... Terminate the inputs of the FactoryAmp to match the output impedance of the head-unit being installed. Doing this effectively dumps most of the electrical noise picked-up by the RCA's & wires to ground while allowing the higher-level audio signals to pass on to the FactoryAmp's inputs.

Click Here: If you don't see pics (goes to Tripod clone site) (updated link: 3/06)


Remove heatshrink from audio pins (notice hidden resistors in black shrink, also 4 new resistors in front



Back of TA-03 showing 4 audio pins - (Red Wire is Right Channel & Top Row is Front)



Unsolder the 4 RCA wires from the connector pins and twist termination resistors onto them before soldering


Add heatshrink tubing (yel) to prevent shorts & add structural support, then tin the ends and solder
them back to the pins

["tin the ends" means melt some solder into each twist first, then when you solder them back to the pins they've
already got plenty of solder so you don't need 3-hands to add more. Use one hand to hold the twist onto the pin
then touch the soldering iron just long enough to make the connection melt back to the pin.]




Add more heatshrink (blu) then twist the ends of the resistors together and tin with solder



Add larger heatshrink to Analog GND wire & solder it to the twisted end of the resistors



After applying heatgun to shrink tubing - (Top Row is FRONT Left & Right)



Completed Mod - tie-wrap all power leads together, then separately tie-wrap all audio & gnd's together



Scosche TA-03 FactoryAmp Noise Fix Mod - Basic Pictorial Diagram & Notes


The output impedance of my head unit is 60ohms at 5vrms, so the 1.9k (1900 ohm) series resistors don't hardly reduce any level and it's easier to leave em in. Basically what you're doing is adding a terminating resistor from each signal wire to ground, closest to the FactoryAmp's inputs. (Ideally you would do this right inside the amp, but this won't be necessary unless you plan on listening to your stereo while driving thru an MRI Scanner or past some military radar dish)


----------------------------------------------------------------------------------------------------------
|__________________SCOSCHE SLC-4 "BLUEBOX" SPECS
|____________( comes w/TA-03 Kit - features & notes below )
|
| * 4-channel HV LINE LEVEL to 4-channel LINE-LEVEL converter
|__( don't need SLC-4 for HU's w/Preamp Outs - Only use TA-03 Conn w/Mod )
|
| * 4-channel SPEAKER LEVEL to 4-channel LINE LEVEL converter
|__( up to 80 watts max per channel )
|__( use SLC-4 together with TA-03 Conn w/Mod - adjust trimpots on SLC-4 to match levels )
|
| * Transformer circuit for noise cancellation.
|
| * Common ground adapter.
|
----------------------------------------------------------------------------------------------------------


So what's with the blue box Scosche provides? Well in an ideal noise-free world you would set the switch to "Line" and plug your RCA's into it and wire the other end into your amp, but if you don't have a HU with high-level preamp outs you can connect your HU's speaker outputs into it (thru the screw terminals) and it will drop speaker-level down to line-level to feed the FactoryAmp. Will you still need to do this mod? Uhm, yeah probably... it's because inside the SLC-4 BlueBox are 4 level-dropping circuits and impedance matching/isolation transformers. What's great about transformers is that they can match the impedance of one circuit to another almost perfectly, plus they can isolate DC path between two devices and only pass the audio signal, but what's not so great is that they can also act like guitar pickups when designed to be connected to high input-impedance amps like ours.

Ever hookup a Scosche SLC-4 BlueBox and wave it around the inside of the dash with the ignition on? Acts like a Theremin doesn't it? That's cuz its transformers are picking up the noise from the data bus running all thru the Celica wiring harness. Ever play with a telephone pickup coil? Almost the same thing.

Notice the TA-03 has 3-ground wires coming out of it. Make sure you connect the ends of the 4 resistors (tied together) to the wire labeled Analog GND in the photos & diagram. The other two GND wires can be tied together and connected to your HU's GND wire. Believe it or not, once you terminate with resistors, your grounding problems will pretty much disappear.

I forgot to mention that when you terminate audio lines with the matching impedance of your HU, your frequency response will probably be restored more closely to what it's supposed to be too. In otherwords if it sounded too bright & tinny before, your bottom end (bass & lows) should come back to life again and you won't have to subtract your treble & max your bass eq settings anymore.

thanks for the help on the board & enjoy your FactoryAmp, I hope it helps...


ps ~ i want to give some credit to EvilED who posted a msg way back in 10-12-2002 about a mod for the factory amp. I found it while searching to make sure the TA-03 Noise wasn't a topic already covered. It just goes to show that doing thorough research pays off if you bother to do it (and no, I didn't find it until it was too late cuz I was lazy too... crap!)

Click Here: EvilED's factory amp mod

Click Here: If you don't see pics (goes to Tripod clone site)

Click Here: For a table of Termination Resistor Values and Final Test Results

Click Here: To jump to post about which GT's this will fit & about TA-02 harness vrs. TA-03

Click Here: Wanna hear a simulation of what the Scosche TA-03 Harness sounds like -without- the mod? [updated 4/2017: sample mp3 file moved to Tripod]
 
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#127 ·
*Repost (need feedback)*

I just recently bought an after market HU, a Pioneer DEH-1900MP, to be exact. I bought the install kit, the ISO/DIN mounts. And was sold a Toyota/Scion 1987-up turbo-wire harness, only to realize that it did not fit the stock radio wire harness. Only to then later realize that, that is because I have the premium sound system, with the stock amp. So I ended up returning the wiring harness, but now i don't exactly know how to bypass the amp myself. I was just wondering If I wanted to bypass the stock amp entirely, would the Scosche TA-03 do the job? Or am i better off doing this mod to use the stock amp with the after market HU? any feedback is welcomed, thank you.

If someone/anyone could PM me or email me with what I should do next. I have the HU on hand and ready to go, I can't wait to get it in, But I don't know what my next move should be. Once again, some help would be greatly appreciated.
 
#130 · (Edited)
To help new visitors to the TA-03 Noise Mod Thread find the latest information more quickly, I've updated both the original mod post and the Table of Termination Resistors post with the latest 411.

The updates note changes in the termination resistor values for the newer TA-03B harness, the compatibility of Bestkits.com BHA8113 harness, and the brand-new Metra TYTO01 harness.

Incidentally, as mentioned in the updates the Bestkits.com BHA8113 may still be using the older-style TA-03(A) connector shell which is much easier to mod than the newer TA-03B. There's one Seller on eBay who seems to stock a bunch of these at a great price. If you want to check him out here's a link to search his store:
Search Store for BHA8113 Harness
 
#132 ·
Well got my TA-03B and even though I was really careful ended up cuting 3 of the 4 wires that connect the resistors when I was cutting the heat shielding. The TA-03B sucks big time and now I have to spend another 30 bucks because the harness is ruined. Be really careful when cutting the shielding back to expose the resistors.
 
#134 ·
I decided to buy the bestkits.com harness since it was only 15 bucks on the link that pacific posted. There have been good reports with this harness and it has the design of the ta-03a which is much easier to mod. I haven't really heard any good reports with the ta-03b. (good luck spartan I hope it works) I could have done it alot easier if my dumb self didn't accidentally cut a wire but unless you have elf hands I would suggest the bestkits over the ta-03b.
 
#135 · (Edited)
I just got done reading all three pages to try to educate myself to the fullest extent. I have the pioneer deh-p6800mp (http://www.pioneerelectronics.com/pna/product/detail/0,,2076_4039_291078777,00.html) and the CD-IB100II (http://www.pioneerelectronics.com/pna/v3/pg/product/details/0,,2076_310069910_307492523,00.html) which allows you to control the I-pod from the head unit. It also charges the ipod. There is an IP-BUS cable that plugs directly into the back of the HU. There are two other wires. One connects to "the terminal always supplied with power regardless of key position." This wire has a fuse in the middle of it with (2A) in parenthesis. The second wire just connects to metal ground on vehicle. Hope that makes sense. I am planning on buying the bestkits.com harness and doing the mod with 620 ohm resistors since the output is 2.2v on my HU. Is having the CD-IB100II going to screw anything up or should the mod work fine. Anyone have a similar setup or and experience or input is welcome.
 
#136 ·
Hmmm well good luck man, I hope I don't have to order another one :\ I just want this done with. And no I don't have Elf hands, I have Spartan Hands!!! ahahahah so maybe ill beat the harness into submission? :p well Idk I have a friend and his dad builds circuit boards for repeater radios, so he's pretty experienced with this stuff, and he should be able to do it. And if he breaks it I'll see if he'll buy another one, ahahahaha well anyway Lemme know how the other harness works out, ber2z.
 
#137 ·
Bestkits.com BHA8113 Harness To Be Tested...

With so many reports about modifying the newer TA-03B being difficult and the price increase from $25 to $35 I decided to see if there's a better solution. When posting the eBay link for the BestKits BHA8113 harness, I also ordered one to test. So I'll post my evaluation here as soon as it arrives and I've finished testing.
 
#140 · (Edited)
Pioneer has always made some nice accessories, and the CD-IB100II iPod interface is no exception. It comes with a standard iPod Cable which you can plug directly into your iPod or if you've got an extra dock handy, plugs directly into the back of the dock instead of your USB cable.

Everything is pulled thru the docking cable so you won't have to run a separate cable to the headphone jack on the iPod. Once your Scosche/BestKits harness is installed, whatever audio source you select on your Pioneer DEH-P6800MP HU will be output thru the harness to the StockAmp.

Nice system, I love how it interfaces & displays the iPod menus on the HU's display. Very cool.
 
#141 ·
Good news Boys & Girls... $16 and a fast shipper later I've got the BestKits BHA8113 harness in my hands, and looks identical to the Original Scosche TA-03 connector & harness. My DMM here at work says the internal series resistors measure 1990 ohms (within +/- 10% tolerance for 2K ohms) and I can confirm the pins are nice & long with heatshrink on them, exactly like my original photos at the beginning of this thread. Also, at $16 delivered there's no BlueBox to drive the price up higher.

Conclusion: In lieu of the Scosche TA-03 (original) which has been replaced by the not-so-easy to work with TA-03B, please use the BestKits BHA8113 harness instead.

Happy Mod'ing Everyone!

~PB
 
#142 ·
Alright, just a little update:
First off I got my TA-03B in today, and insisted on getting my radio in. So I went to a friend's house, his dad makes circuit boards for repeaters, so he was much more experienced than I was, and thus made it a lot easier. So if you haven't done this kind of thing yourself before, I highly suggest making a friend whose father is an electrical engineer :D It can be done, from what I saw, him actually doing the work it wasn't that hard, you just have to follow the original plan, and be very careful. So i got it mod-ed, with a 130 and 470 ohm resistor combination, to make it 600 ohms, close enough to what I needed to make it exactly 500 mV (647.3 ohms) so the mod-ing went smooth. I have some pics if anyone is interested, I forgot my actual camera so there $hitty quality phone pics, but better than nothing :\
Installation was another story, my HU only had two RCA out-puts for the rear speakers, so I was forced to use the blue box. At first I wired the speaker outs into it incorrectly, but then just swapped em, and that was fixed. I still haven't mounted the blue box securely, still possibly tuning it. But with the mod-ed harness and Blue Box, I didn't hear any buzzing, humming, or any noise at all, but maybe I wasn't listening well enough... Anyway the only difficulty I have with the blue box is that if I flip the switch to "Factory Amp" or "Common Ground" there's no sound, so I left it on "Line out" and it's fine.
Other problem, the rear speakers seem more timid than the front speakers, having to turn them up a lot more than the front speakers, to equal the volume. Not sure if the resistors are causing that, and if so, why hasn't it affected the front speakers? So If someone could offer some advice or insight on that problem, that would be greatly appreciated.
Another final problem is a "pop off" idk if I'll just have to get the SPSOFF to solve that or maybe some re-wiring can help. Once again, thank you all for your help and feedback.
 
#143 · (Edited)
First, congratulations on getting your TA-03 modded. Second, I'm not sure I understand when you say "my HU only had two RCA out-puts for the rear speakers". Full use of the TA-03 harness & Toyota 20-pin connector involves connecting 4-RCA's for FrtL + FrtR plus RearL + RearR.

If your HU only has 2-RCA's (LEFT + RIGHT), you could try using an RCA Y-Cable plugged into each channel and connect one leg to the front, one to the rear, and repeat using another Y-Cable for the other side, but the level may be too low since you'd be terminating each channel thru the harness twice, aka: "double-termination". If you have to crank the HU to max to get decent level, you'd basically have to double the value of the terminaton resistors used. For example: instead of 600-ohms use roughly 1000-1200 ohms to conteract the double-termination. (I'm too tired to do the math, but technically the 1.9k series resistor helps prevent this from having the same effect as a true double-termination, so doubling the termination resistor value should easily compensate for the loss.)

And guys, I can't overemphasize the importance of throwing the BlueBox out the window if you want to connect an aftermarket HU to the Toyota StockAmp. I never went into all the reasons why it's a headache, but yes as you're experiencing, distortion of the frequency response curve through cheap passive capacitance/inductance/transformer-staged coupling is one of the side-effects when compared with using direct-coupling which is what the harness uses. It is -not needed- for connecting a 2/4-channel LineOut HU to the 4-Channel StockAmp, and in fact will only add noise and alter the frequency response of your HU's clean signal.
 
#144 ·
Hey guys, I really don't know much about electricals. But since I'm going to put a new kenwood HU in, I'm trying to figure out what I need in order to get it to work on my 02 gts.

So from the HU manual, I got these specs...
Preout Level (V) : 2V/10k ohm
Preout Impedance : 600 ohm
Speaker Impedance: 4-8 ohm

So I'm looking at this thread. Since I have a 2V preout, it seems like I'll need 633 ohms resistors (+16% for ta-03b). But my question is, what does the all the extra ohm values mean on my specs? So say Preout Impedance, since it's at 600ohm, do I take that into the equation meaning I only need to add 33ohms resistors to get the 633ohm recommended in this mod?

And also, what does the 10k ohms from the "2v/10k ohms" spec mean? Any help would be greatly appreciated.

Thanks in advance guys!
 
#145 ·
Just lookup your HU's HV Output Voltage in the table and use the resistor value listed in BOLD.

The "active impedance" of a signal source is measured in ohms but doesn't necessarily match that value when measured with an ohmeter. For example your HU has 600-ohm PreOuts, however won't necessarily measure 600-ohms across the PreOut's when measured with an ohmeter.

This is because "impedance" is a complex quantity which represents a circuit's opposition to an AC (alternating current) signal and its phase. It's calculated mathematically.

The receiving-side of the system (StockAmp) also has an impedance (approx. 1M aka: 1 million ohms) which is a total mis-match of impedances. Therfore we couple the source & desitnation thru an L-pad antennuator network formed by the 1.9K series resistor and a mathematically chosen terminating resistor whose combined value is equivalent to the output impedance of your HU, placed as close to the input of the StockAmp as possible (in this case inside the TA-03 or BestKits harness).
 
#146 ·
Wow, that's as comprehensive as any answer can possibly get! Thank you for taking the time to explain that to me! I guess I have one final question for you. Say I cannot find one 600ohm resistor, can two 300ohm resistors soldered together in parallel on the harness achieve the same result as one single resistor of equvialent impedence?
 
#147 ·
Thank You!

:wiggle: Okay I just built my carputer and slapped that joker in my GTS. I measured the output voltage of my soundcard and got 2.2V. So I needed to drop it to 500milivolts... easy enough. I first purchased the Scosche TA-03B harness and modded it accordingly. Yes, using the new resistor values- but had whine. Boooo! I believe it may be because of the structural compromise of the connector which is necessary to mod that one. I cut away the bare minimum to access the pins for soldering with a fine tip iron, used flux etc. But the connection didn't seem secure. I then bought the BHA BestKits harness and modded with 560 ohm resistors and BOOYA no whine and perfect audio. PS... an 8 inch touchscreen really fits perfectly in the dash. Thanks for all the help in ere folks!
 
#148 ·
cdnsir said:
Wow, that's as comprehensive as any answer can possibly get! Thank you for taking the time to explain that to me! I guess I have one final question for you. Say I cannot find one 600ohm resistor, can two 300ohm resistors soldered together in parallel on the harness achieve the same result as one single resistor of equvialent impedence?
You should put the resistors in series. Heat shrink over both for support.
 
#149 ·
Ok I'm confused.

2000gts getting alternator whine.

Line out level/impedance
2.5V/20k ohm

I have the metra harness from Crutchfield (Never had to deal with these new systems with my old cars 'sigh' )

How can I do the calculation if the I don't have any resistors in the harness? If I put in 0 I get 0.
 
#150 ·
Scroll up a few posts and order the BestKits BHA8113 harness from the eBay search link I posted prevously. He still sells them, but now they're only $9.95 As mentioned before, the Metra has no series resistors so it's useless unless you want to take the time & trouble to add them yourself.

The BestKits BHA8113 Harness is identical to the now-discontinued Scosche TA-03A originally used in this mod and is the only harness I can recommend to take its place. Good Luck.
 
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