> Is it possible that there is some signal ground that is different that
> chassis ground that will hurt something else on its circuit once the cig.
> lighter is used?

Hey Tom

I agree with Alan - don't see much reason for them to put ground in the fuse
box. Unless you absolutely know that it is hard-tied to ground, I wouldn't
use it.

There may be a difference in where you tap your ground, depending on what
type of equipment you want to install:

For instance, if you need ground/power for a two way FM radio, the best spot
is the ground/power lug of your battery. Tapping it anywhere else and you'll
have currents with other devices in common. Quite often you'll hear the
alternator's generated AC component superimposed on the transmitted signal.
On the other hand, AM/SSB transmitters or audio components (Radios and amps)
could also have similar artifacts in their audio, but may be less noticeable
because of the basic technology used. I had a Saab once that had a slight
alternator whine on its speakers, regardless of my volume control setting --
since it was a relatively low power device, a simple choke killed the noise.

If you are running something like a GPS or PDA, grounds don't make much
difference since devices like that usually run indirectly off the 12V power
through a regulator or switching power supply -- these introduce typically a
lot of isolation and so any noise picked up will not make much difference.

What are you trying to hook up?

Regards,
Remco