99 GMC suburban Rear speakers dont work. I have a 99 GMC suburban. I just replaced the AC Delco stereo head unit with a pioneer. Now the rear door speakers do not work. I have heard i need to bypass the factory amp. If this is true, how do i do that?

Either that speaker is not connected or, the speaker is blown. To test: Disconnect that speaker from the stereo and, using a 9volt battery, tap the speaker's + and - to the battery's + and -. You should hear a "pop". That would indicate that the speaker works. DO NOT connect the 9 volt battery to the stereo side of the speaker wire!!!!

There could be several reasons why the head unit for your car does not work. The most likely issue is that the head unit is not compatible with your stereo system. You can consult your vehicle owner's manual for speaker issues.---------------------------------------------------------------------------------------
Diagnostic VAG

Good chance that the radio power supply to those speakers have gone bad. There common for the GM Delco head unit, when the head unit get's hot. The solder get's weak and then you have what they call a cold solder, causing a bad current flow to the power supply to the rear speaker wire harness.
If you like to keep the stock head unit, you can remove it and have a electronic shop repair the head unit. Or you can go to the salvage yard and see if you can locate an other head unit for around $50.00, you should be fine with the year of your Cavalier, the 2001 and newer head unit was mated with the car's Vin number through the ECM to have it function.
Thank you for using fixy and good luck.

Check the right wiring diagram for all speakers...



Hope this help; TY for using Fixya (remember cmment and rated this).

if you have a wiring guide for your deck, take a look at it and see what your rear speaker + and -'s are, connect them accordingly to the wiring guide in the link and your speakers should work, if not, the wires running to the speakers are probably damaged. if thats the case, go to a dollar store and pick up some speaker wire, and run it under your panels, or carpet, what ever is easier for the particular make.

Find a blue wire on the wire harness to the truck and connect from the blue white on the radio. this will turn on the factory amp that runs the rear door speakers

sound like the head unit's out put mosfet is going bad, but i have also ran in to this problem when it was a speaker wires shorting out. so first check the connection on your rear speakers.

the 99 suburbans have a factory amp to run the rear speakers bypass this amp or replace it.

This is an amp problem but you also need to confirm that there are no burnt wires and cut fuses.

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You need to attach the blue wire on the stereo harness to the blue and white wire on the car adapter harness. they installed a small amplifier to power the rear door speakers and unless you connect those two wires then the speakers will not work.