Headlight/tail issues

[AR67GTX]

1966 Plymouth Satellite. Just installed all new electrical harnesses in dash, engine bay and headlights and have a few issues to troubleshoot. First one I tackled is the headlight. Headlight switch is the one in the car previously and worked. Dash lights work. Turn signals work.

Pulled them loose from the buckets and checked for power with test light. Shows power to all 3 terminal, both sides. This was testing on the exposed copper leads into the lights. Changed white ground lead to new location with ground washer - no change.

Checked battery voltage - around 12.5 v

Pulled bulb loose and with jumpers tested it directly to battery - lights up fine.

Tested voltage at exposed contact on the bulb after plugging it back in to harness - 11.7 v on all. That includes the white ground lead. I guess that’s right - my brain is too cluttered and dull right now?.

Got out the old harness to check orientation of wires on plugs of new harness. Slight difference in how ground are run on the harness but every lead is in the correct position.

Too puzzled to go further today. I think tomorrow I will rig up three short jumpers from the plug to the bulb spades and see what happens.

These are new Sylvania halogen bulbs. Any chance 11.7 volts is too weak to fire them. Not ready to restart the motor yet.

Any idea what’s going on here?

 

[1toolguy]

The bulbs may be slightly dimmer at that voltage but should work.

 

[AR67GTX]

Figured it out - bad ground. Ran a jumper from the power power side of the plug to the light contact spade for low beam and a jumper from ground contact spade on the bulb to an exposed bolt shank on the radiator support and it lit up.

I had the ground wire connected to one of the screws mounting the headlight bucket, which was a bare galvanized surface but it must not be grounding out. The ground lead is short so I’ll run a jumper to somewhere on the radiator support to better ground it.

Now on to the tail lights

 

[AR67GTX]

Wasn’t the ground connection as it turns out. When M&H crimped the ring ground terminal on to the harness lead, they only crimped it to the insulation and not to the conductor wire.

Now to figure what powering (back feeding) my curtesy lights inside, why no tail lights and why no windshield wipers. Man I hate electrical.

 

[Rusty 72]

The lack of taillights is probably a ground issue as well. Do you have Brake lights? if you do then that eliminates a bad ground at the bulbs. If no brake or tail lights, I would start looking for power at the harness connection near the drivers door and work my way back.

 

[AR67GTX]

Yes, it was a ground issue to.

Interior curtesy lights (console & pillar) are my biggest puzzle now - they are always on. The door switches and lighting switch don’t have any effect on them so must be getting back fed from somewhere. Guess I’ll pull the fuse one on the cigarette lighter (feeds door switches I think) and then try another light switch to see if I can isolate the issue.