i installed a new cd player in the car by re running all the wires to the new deck and now when i turn it up loud not as loud as it would be with the stock radio its starts to break up like its not grounded properly. i checked the ground wire and everything is connected anyone knows whats wrong? is it because of the stock amp if so how can i take that out and have the new head power all the speakers. its a jvc kameleon and im pretty sure it can power all the speakers thanks for your help everyone

You can use the existing factory speakers, driven by your new head-unit, but it's a little complicated. The factory amp has, inside it's case, passive crossovers for the factory speakers. That is, the factory amp has 10 speaker outs that send the correct (filtered) frequencies to all of the speakers in the car.

So what you have to do is bypass the amplifier section but hook your head-unit speaker-outs up to the factory crossover inputs (inside the amplifier case). A very cool contributor on this board, Anthony, has detailed the procedure. Below I've linked a link to a link (or something like that) of said procedure.

...per this link from Anthony (thanks again!), keep the factory speakers and crossover but bypass the factory amp and use your head unit's amplification. I think that's a swell solution, since running the power from a nice deck through the PWR1 or OEM-4 to use the (not so great) factory amp is kind of a waste.

I cannot remember who asked for it but here's how I connected to the factory speakers using the original booster amp. This mod is fully reversible in the event you want to move your stereo to another car.

Connect to your factory speakers through the booster amp board and save! ('90 model with 10 speaker setup referenced, others may differ)

From experience with previous bimmer stereo setups, I determined the head units are cheap but the factory speakers are great as long as you keep the power (read: BASS) down. The best way to achieve this is to use an active crossover, 4 channel line level amp (30-50W/ch) and a mono amp for subwoofer. Of course you need a differtent head unit with RCA pre-outs...

Connect to the booster crossover board after removing the power amp module:
1) Remove cover from booster and remove equalizer module and its housing.
2) Remove the screws securing the heatsink, then unplug the power amp assembly from the main board.
3) Remove the amplifier section from the heatsink.
4) Attach the 4 pairs of output wires from the new 4 channel amp to the pins shown observing that + and - are all oriented the same way. (I soldered the wires low enough so the whole thing can be returned to stock) Each conductor is attached to a pair of pins on the connector.
5) Re-attach heatsink
6) Cut power wire to booster to use as feed to crossover. The white wire is soldered to the inside PCB and provides the "turn on" signal for the amps and xover.

You now have the benefit of carefully engineered speakers and wiring and you only had to run one wire from the head unit.

Thanks Anthony Doyle