I'm sure this has been well documented, but after searching 'Mud and Google and finding what seemed to me like unclear information, I thought I'd post my results here.
I installed a Scion head unit with iPod controls in my '93 80 series and immediately had a multitude of problems. The speakers sounded like they were blown, I had a low whine at all times which got much worse when I turned on the lights. It was also affected by the dash ligh dimmer switch. After trying several different things, I finally threw up my hands in frustration. I began searching around and came to one of these conclusions:
1. I had a ground loop somewhere
2. My head unit was bad
3. I needed line filters
4. I'm a moron
Then, last night I came across a post here on mud where others were having very similar problems. Several posts mentioned disconnecting the factory amp, but there seemed to be conflicting information about how to do this, if bypass wiring needed to be installed, etc. But, one post included an excerpt from another source (crutch field maybe) that seemed to indicate that Toyota had run parallel wiring to each speaker, one set through the amp, one bypassing it. So, on that information, I pulled the glove box and disconnected the two grey plugs attached to the amp. And, like magic, it worked! My stereo once again sounds clear and good (well, as good as a 20 year old stereo can sound).
The Scion head unit uses the two grey plugs instead of the larger white plug used by the factory unit, which bypass the amp. However, the factory amp is still sending output to the speakers which causes the aforementioned interference.
Here are some pictures of the amp and the cables I disconnected. Hopefully this can help someone else in my position.
I installed a Scion head unit with iPod controls in my '93 80 series and immediately had a multitude of problems. The speakers sounded like they were blown, I had a low whine at all times which got much worse when I turned on the lights. It was also affected by the dash ligh dimmer switch. After trying several different things, I finally threw up my hands in frustration. I began searching around and came to one of these conclusions:
1. I had a ground loop somewhere
2. My head unit was bad
3. I needed line filters
4. I'm a moron
Then, last night I came across a post here on mud where others were having very similar problems. Several posts mentioned disconnecting the factory amp, but there seemed to be conflicting information about how to do this, if bypass wiring needed to be installed, etc. But, one post included an excerpt from another source (crutch field maybe) that seemed to indicate that Toyota had run parallel wiring to each speaker, one set through the amp, one bypassing it. So, on that information, I pulled the glove box and disconnected the two grey plugs attached to the amp. And, like magic, it worked! My stereo once again sounds clear and good (well, as good as a 20 year old stereo can sound).
The Scion head unit uses the two grey plugs instead of the larger white plug used by the factory unit, which bypass the amp. However, the factory amp is still sending output to the speakers which causes the aforementioned interference.
Here are some pictures of the amp and the cables I disconnected. Hopefully this can help someone else in my position.
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