So I believe I have a short...

it's a '77 F-100 Stepside with a 3 speed cruise-o-matic tranny powered by a 5.0L 302C.I. V8 (2 Barrel Edelbrock Carb)

All of my rear lights and turn signals worked fine... untill out of nowhere they changed to this...

When in Park, no rear lights work (including break, running) AND if you put one blinker on, they both light up...

When in reverse.... Brake lights work... running lamps do not, turn signals do work.

When in drive... Not a damn thing.

Also, when the rear lights/turn signals work, the running lights up front become very dim....

They have worked for the last x amount of years.... At the same time, the "Brake" light on the dash wont even illuminate when you go to start it... which it should.

So i take it that it's a short? Any idea where to start? I searched every wire and everything is hooked up. Nothing was severed. Never had this issue prior.... HELP!

 

Do the headlights work normal and the marker lights????

 

Yes the headlights stay lit and work fine. So do the markers...

 

check in your steering column to make sure you dont have a rub thru or a bad connection there maybe even some corrosion. just a thought

 

Then I would assume its in the multifunction switch!!

 

I'm willing to bet that somewhere in the harness feeding the rear lighting, you have a chaffed harness where it rubs something .... or animal induced damage .... or you have some bad ground, or both. Nothing for the rear running lights is in the steering collumn even though the brake and signals do have some roots in the turn signal switch.

My bet is on the chaffed harness resulting in a short or shorts and some sharing of grounds. Also, check closely where wiring runs through steel like firewall rubbers, etc .... (and check the harness in the steering harness where it exits or is held in place by a metal clip / clamp).

The headlights growing dimm when the rear lights do work sounds like a short draining some of the available juice to ground. The headlights also have no roots in the steering column or signal switch but a short elsewhere would still affect them. These trucks have maybe 60-63 amp alternators when new.

 

.. then it should be called the multi-malfunction switch!