Running Lights Wiring Question

[tsubaki]

Originally Posted by greateastern

I have grey and black wires, the greys go to the switch the blacks I will trace out after work. When I put the meter to the 12v dc wires the meter reads -12.5v dc with the red meter lead on grey and the black meter lead on black. then I change it around and I read 12.5v dc no more - so i figured the grey wire is the ground wire, neg, to the meter. Does that make sense?

Yes that should be the case, and is this with the light switch on and both bulbs burning?
There are a lot of variables, if someone derived the negetive from a dashlight panel and a wire broke or bulb blew, this could create a whole number of funny readings.
First try to localise the ground from the lights to their source, as to where they are connected.

You wouldn't believe the mess created by the "mechanics" on a brand new boat that my neighbor bought.
Most all of this is simple but when you get to thinking too hard it makes a bigger mess.
Rewiring does give a lot of piece of mind.