Okay, if you got one then you know it's hard to find info on it. Here are a few things I have learned about my 1992 Prevy. First off, if you can't figure out how to remove the old stereo, don't rip anything out yet........here's how to do it.
https://carstereohelp.com/stereoremovalToyPrevia.htm
Okay, next off, there IS a factory amp installed. if you choose to ignore the amp, your new stereo/speakers will sound like crap. The REAL location of the amp is under the passenger side dash. It's real easy to get to, close to the floor, just look up the passenger side dash and it's right there. Looks like a black metal box, with 2 or 3 wire clips connected to it.
Unhook ALL those wires, and remove the amp (And pitch it as far down the street as you can). In the stero cavity, where the radio goes, there are 3 wiring harness's. One for the antennas. One go's to the amp. One bypasses the amp.
There are 2 antennas, the retractable one, and the back glass one........use both. The stock radio is hooked into the amp harness, don't use that one anymore. You want the bypass one.\
If you have any questions I'll try to answer them if I can.
Great information, thanks for the post.
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Jeff
Velocity Custom Home Theater
Mobile Audio/Video Specialist
Morden, Manitoba CANADA