90 chev PU amp cuts out

1990 full size chevy pu.
has the factory 3 piece EQ cassette stereo.
Thr front speaker outputs go to a line out to the 4 channel amp that powers the front dash and the subs.
The rear speakers are powered by the GM head unit.

The amped speakers are now cutting out. This is a 10+year old install. Give the truck some throttle and the amps garbles out. Apply the brakes it garbles back in. Stop and park the amp plays GREAT. Now if you rev the engine it garbles out. Put it in gear in Rev or drive and apply a little throttle the amp cuts out.

Tested ground. from the amp tp the radio and again both places to the battery. Ground is good the 12volts stay constant too.

I checked the speaker leads.i disconnected the subs and their RCA's just using the front speakers, it would still garble. ran new temporary front speakers leads, It still cuts out. Tried a new rca cable set. same cutting out. tried a new RCA converter still cuts out.

OK any ideas?
what am i missing?

Check the internal solder connection at the power, ground, remote terminals ? Also, check to see if there are cold solder points at the RCA. Not saying that this is what the problem is, but this will help you narrow down what it isn't.

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Jeff
Velocity Custom Home Theater
Mobile Audio/Video Specialist
Morden, Manitoba CANADA

I fingered it out.

It was the freaking alternator!

It worked great on battery,
It worked great at idle in gear,, engine slowest speed.
give it any rpm and it began cutting out and the more rpm it went silent.

removed the belt and enginer speed had no effect
swapped out the ALT and its all good again.

It showed 14 volts of charging though, but had some kind of AC output i am guessing.

Keep this experience in mind on a goofy problem like that.

Im glad you found the problem. Ive had the same exact problem stump me for days on older cars. I only figured it out when the voltage guage started reading low.  You learn from your mistakes right?