Electrical Help needed - Tail Lights and Gauge Cluster

[rean1mator]

Hi All,
Just picked myself up a '74 Bronco Ranger last month and would appreciate some help on some electrical issues that I'm having.

Cluster Problem:
Originally none of the gauges were working and searching through the forum I narrowed it down to a bad ground. I pulled the cluster out to refurbish it and I fixed the ground issue and both temp and oil pressure started working. However after the install back into the dash two new problems popped up. When I turn the head light switch to on the following occurs: 1. both temp and oil pressure indicator moves moves to the maximum position 2. when I turn the turn signal to the right it does not blink but stays lit.
When I turn off the head light switch everything goes back to normal.

Rear Tail Lights:
1. left and right turn lights work.
2. Tail light does not work when the head light switch is turned on.
3. Brake lights do not work.

All the connections seem to be fine and made sure all the grounds for the rear are ok.

Any ideas?

 

[Viperwolf1]

You still have a ground problem at the cluster.

See if both front and rear turn lights are on with the indicator. Good chance one is not.

Check for voltage at rear tail lights and check bulbs.

Check for voltage at brake switch.

 

[Steve83]

...indicator moves moves to the maximum position...

Don't do that again until you find & fix the problem. Putting a full & steady 12V across the gauges can burn them out.

...turn signal to the right it does not blink but stays lit.

That COULD be due to a burned bulb, but it could also be a weak ground.

Tail light does not work when the head light switch is turned on.

That's certainly a weak ground.

...all the grounds for the rear are ok.

I don't think so. The "ground" isn't the end of the circuit; it's just a way for the current to reach the battery negative post. You have to provide a continuous solid path from each "grounded" device all the way back to B- in a way that will handle all the electrical current on the truck. Your symptoms suggest your body tub is NOT connected to the battery black cable. I recommend running a new ~8~14ga black wire from the block ground bolt to the body tub using a serrated ring terminal (one that will penetrate paint & rust to make a connection to the sheet metal). Use a locking nut &/or red threadlocker to make sure it stays tight to the body forever.

It wouldn't hurt to run another one to the frame so that the fuel tank sender, a trailer, & any bumper-mounted lights have a solid current path. If you run a winch, the frame ground needs to be the same size as the battery cables.