First a little background:

My brother purchased a stealthbox from subthump and an alpine type R (dual 4 ohm model) for his '01 TA. After wiring the amp and installing the sub in the car we turned on the stereo to test out the setup. Unfortunately, the sub wasnt hitting at all (Tuesday). Being that it was 1am and he had to work in the am we called it a day and decided to troubleshoot the next evening (Wednesday). After rereading all manuals and verifying everything was connected we start the troubleshooting process.

I previously had subs setup in my 00 TA before the stereo was stolen so I had the idea of moving his sub/amp/HU to my TA to eliminate the wiring as a possible cause. Everything works beautifully in my car so we move everything back to his and start troubleshooting the wiring.

We started by running a set of RCA cables from the Amp directly to the HU (hanging in mid air) and the problem did not correct itself. Next we decided to check the powerside of the amp so I grab my trusty meter.

This is where we noticed a strange problem. With the stereo on and amp connected I tested the voltage between the 12VDC and the ground...then the remote and the ground.....both read 6VDC. We disconnected the cables from the amp and I tested them directly (thinking maybe the leads on the amp were causing a draw) and i read 12VDC.

So my thought "ok, bad amp?" and rewired everything to my car and tested power...I read 12VDC on my leads regardless of being connected to the amp or not..

So in an attempt to test my brothers battery we connected the positive and ground from the amp to my GFs battery (her car was closer to his). The sub starts putting out bass the way its supposed to.

This afternoon my brother goes and buys a new battery because he has been having other electrical issues and thinks he may not be putting out enough amperage but it doesnt correct the issue.

what could cause this drop in voltage?

 

bad ground IMO

if it was just on power wire Id say maybe bad connection at fuse holder

try measuring from positive wire at amp to the negative terminal at the battery under the hood

 

It did in fact turn out to be a bad ground. It was strong enough to complete the circuit but not push the sub. After checking against a bolt out in the open we put it in the old spot and continued to wiggle the connection until everything stayed running.

Thanks for your help