Can i check my ground with a volt meter?

Question

I have two amps grounded to where the tail lights are grounded in the trunk, but ive heard from several people that thats not a good ground, and some said that it is, but wherever it is can i check it like this (put a volt meter to the terminals of the amp and try to read 12.3 volts(which is my batterys voltage) if not is there another way using a voltmeter

Answer 1

You can do it using a long jumper lead.  Set the meter for DC volts.  Attach one probe to the amplifier's ground terminal.  Connect the jumper lead to the negative battery terminal, and connect the other end of the jumper to your second probe.  (A jumper lead is just a length of wire with alligator clips at each end.  You can make your own, using a few feet of speaker wire and crimp-on alligator clips from the hardware store).

Turn on your system and set it at maximum volume.  Watch the voltage on the meter.  (A meter with a recording function, or a min/max setting, is very useful here).  What you're seeing is the exact amount of voltage lost through your ground wire, ground connection, and the chassis of the vehicle.  Lost voltage is caused by resistance in this part of the circuit, so if you have a poor ground connection, it should show up here.  If your voltage reading stays below 0.3 to 0.5 or so, then you shouldn't have anything to worry about.

The systems needs to be on and playing during your voltage tests, because voltage drops are caused by a combination of resistance and current.  If the amp isn't playing, then there's no current flowing in the circuit, and no voltage drop.  You need to have it playing as loud as you ever listen to it to get an accurate test.  Don't endanger your speakers, though.

You may find someone suggesting that you use the "resistance" or "continuity" function of your meter to test your ground.  Don't bother with this.  Ordinary multimeters are very unreliable when testing very low resistance levels, and it doesn't take much of a resistance to cause a serious voltage drop in an amplifier power line.

Of course, another possible problem with your ground is that it might cause noise problems from the shared accessories.  Sit inside your car and listen to your system at a normal level.  Find a very quiet passage (or just pause the CD).  Listen to see if you hear any pops or hissing in your speakers when you turn your lights on and off, use your turn signals, or press your prake pedal.