What's the difference between a common ground and a negative ground chassis?

[bmacd]

i'm installing a car stereo on an '89 crown victoria for a friend. Not only did i have to run wire straight to the speakers (as opposed to using the factory harness), but i'm having trouble with the amp. If i run a constant 12 volts (red battery terminal) and get a ground from a metal spot in the trunk, i can only get ~5-6 volts. Running a negative AND positive wires directly from the battery solves this problem, but i'm not sure i want to run one more wire (ground wire) from the engine bay all the way back to the trunk again. The space we had was tight enough as it was. Is there any other solution? I've already run a positive cable from the engine bay to the car, as well as all the speaker-level/RCA inputs/outputs. I have the negative wire grounded out in the trunk.

-=bmacd=-

 

[bmacd]

ttt

-=bmacd=-

 

[Pepsi90919]

what does this have to do with the thread title?

btw try finding a better ground somewhere.

 

[Tominator]

The words 'common ground' only refer to the chassis or body of the car as a common place to find a ground. It might mean to find a point in the trunk where the wiring harness is grounded to the car. That would be a 'common' place to ground the wires.

The term 'negative ground' means that the minus side of the battery is ground. Back in the fifties many cars had a positive ground. the plus battery terminal was grounded to the chassis. Some foreign makes used a positive ground, or earth, into the sixties.

Newer cars have very good paint and rust proofing and this can make finding a true ground difficult as the coatings also make good insulators or in your case add enough resistance to lower the voltage.

Scraping any paint or rust from the area before attaching the grounding wire might help. If you do that use silicone sealant and smear it over the area to keep moisture and air from causing corrosion. The best wat to insure a good ground is the way you've already discovered.

 

[Analog]

Originally posted by: Tominator
The words 'common ground' only refer to the chassis or body of the car as a common place to find a ground. It might mean to find a point in the trunk where the wiring harness is grounded to the car. That would be a 'common' place to ground the wires.

The term 'negative ground' means that the minus side of the battery is ground. Back in the fifties many cars had a positive ground. the plus battery terminal was grounded to the chassis. Some foreign makes used a positive ground, or earth, into the sixties.

Newer cars have very good paint and rust proofing and this can make finding a true ground difficult as the coatings also make good insulators or in your case add enough resistance to lower the voltage.

Scraping any paint or rust from the area before attaching the grounding wire might help. If you do that use silicone sealant and smear it over the area to keep moisture and air from causing corrosion. The best wat to insure a good ground is the way you've already discovered.

right on the money.