Don,

With your test light....

Remove headlight.

Remove plug from headlight.

Clip ground alligator clip to headlight bucket.

Turn on ignition.

Turn on head lights.

Probe headlight socket until test light lights.

Note wire color feeding that hole in the socket.

Turn on high beams.

Probe socket until test light lights.

Note wire color feeding THAT hole in the socket.

Turn off lights, ignition.

The third wire on the socket? That's the ground.

Easy peasy.

Assuming left headlight, s/b white to high beam and white/black to low
beam. DIN says grounds are brown. Pretty much always. Right headlight:
yellow and yellow/black respectively.

Jim

Never to wrong others takes one a long way towards peace of mind.
--Seneca

On Jun 9, 2012, at 2:10 PM, Don Hanson wrote:

>   When I go to identify the Ground wire in the wiring to the plugs
> for my
> headlights...How do I determine that?   Can I do that with my test
> probe
> light, the one with an alligator clip and a wire with a bulb and ice-
> pick
> arrangement on the other end?  Or if I use my digital multimeter set
> at 20v
> as a tester, I should get a 12. xx v reading (headlights on, of
> course) but
> should that be a + reading from the power source and a - reading
> when I am
> on the ground, or how?