Help with Stock radio HU / amp

[Who]

Hello I need some help on getting some tunes back in my car. I want to keep the Stock HU. The radio has power. The original underseat amp UM-173 was corroded and I got no sound out of the speakers. I got a used amp. Mistakenly it looked the same but the number was different, um-201, and the color codes on the harness are different.
Everything plugs in just fine and I can hear the radio now but I have to turn up the volume all the way up to just hear it at a very low volume. The fade, Balance, Dim, Antenna all work. The only issue is the volume.
I have used this helpful link from ishii http://www.supraforums.com/forum/showthread.php?t=391532 but I am confused about the color assigned to the wires vs the pin positions. My Harness is factory and never been hacked.
Photos with descriptions are provided.

Here is my setup.

1. 1989 supra with cd / radio / tape / externally amped 14 pin plug at back of radio and 8 speaker setup
2. A voltmter and basic knowledge of schematics.
3. A replacement amp with wire colors that do not match the old amp

 

[Dan_Gyoba]

The wire colour is relatively unimportant as it would be different for different year/makes, however, Toyota is very good about making sure that if it plugs in, it's the right connector. If the connectors are the same, then the amp will work. It may be a different wattage rating than your original, but it'll still work out.

The standard Toyota plugs go into the amp, and the amp powers the head unit, IIRC.

 

[Who]

The wire colour is relatively unimportant as it would be different for different year/makes, however, Toyota is very good about making sure that if it plugs in, it's the right connector. If the connectors are the same, then the amp will work. It may be a different wattage rating than your original, but it'll still work out.

The standard Toyota plugs go into the amp, and the amp powers the head unit, IIRC.

When I say the volume is low I mean very very low at full volume. Almost sounds like there is a wire crossed. Well all the plugs do connect and the radio powers up and the balance and fade functions work. So from your post I can assume that the amp is bad or the HU is bad.
Can I bypass the amp and replace the HU with another toyota non-amplified HU and connect to the standard toyota plugs behind the dash. Remember I have a eight (8) speaker system (ohms, wattage, ect.)?
I am leaning torward bypassing the factory amp only to eliminate another variable in the system and it seems that the factory amps are prone to failure.
By the way I visited your website. Nice car, and Nice detail work. High five to you.

 

[Dan_Gyoba]

Can I bypass the amp and replace the HU with another toyota non-amplified HU and connect to the standard toyota plugs behind the dash.

Absolutely. You can have my stock 1989 non-amplified head unit, if you pay shipping, though it's cassette only. It's been sitting under my desk for years now, and I'm never going to put it back in.

If it plays at all, then it's gotta be connected right. The unamplified signal will not drive speakers.

I did have a diagram showing the pinouts of the amplifier somewhere. I suppose that it should be possible to substitute an aftermarket amplifier with that diagram. You can't use the amplified factory deck without an amp, though.

P.S. Thanks for the compliment.

 

[Who]

Absolutely. You can have my stock 1989 non-amplified head unit, if you pay shipping, though it's cassette only. It's been sitting under my desk for years now, and I'm never going to put it back in.

If it plays at all, then it's gotta be connected right. The unamplified signal will not drive speakers.

I did have a diagram showing the pinouts of the amplifier somewhere. I suppose that it should be possible to substitute an aftermarket amplifier with that diagram. You can't use the amplified factory deck without an amp, though.

P.S. Thanks for the compliment.

I might take you up on that offer. I have a old connection at the local junkers so let me try locally first.

I think I am going to try and go to the stock non amplified setup eliminating the pesky underseat factory amp. On the flip side I was thinking along the same lines as you were. With the factory underseat amp providing me with the power and speaker line levels in and out why couldn't I put another small amp under the seat and patch into the speaker line levels. I would have to find the ohms of the factory speakers. Sometimes the manufacturers use some funky setups as far as ohms go.

Here is a link I found with the pin diagram for toyota radios. I thinks this will help me out immensely.

Credits to: ishhi
http://www.supraforums.com/forum/showthread.php?t=391532