Hey there guys, new to the forum and working on dents...I have a 73 F250 with a 78 cab and front clip, and I cannot figure out where my problem is. I have headlights and my passenger side front marker light works but the other three marker lights, turn signals, cab lights, interior lights and brake lights all don't work??? I have replaced all the fuses and bulbs and don't know what step to take next...thanks for any advice in advance!

 

Buy a hand full of ground straps, and install them in various locations between the body and frame, and 1 each engine to frame and engine to body.

 

Alright, I will give it a shot! Thanks!

 

And to make sure that work is rewarded, make sure you have a main ground from the battery to the body.
There should be one ground strap between the engine (back of the intake) and the body (firewall) but starting with the battery-to-body is always a good thing.
The factory put one there, but often as not they get left off when the first battery cable is replaced with a store-bought one.

Typical location would be from the negative lug on the battery (obviously!) to the inner fender where the starter relay/solenoid/thingy is mounted.

Back to the lights, the sidemarkers themselves are notorious for going out. Sometimes only needing a nudge or a kick to get lit again, or when they're old enough they sometimes need replacing.
New plastic sockets are readily available. But check yours first by pulling them and the bulbs out to check their condition. I assume you've already done that, but it's worth mentioning.

Grounds are always a good first step with any old vehicle. But it sounds like you actually have several issues going on at once. You could be fighting a bad brake light switch, and/or a bad turn signal switch, and/or burned out bulbs and/or rusty fuse contacts, etc.
Since you pulled and reinstalled the fuses, that's a good thing because they often build up resistance just sitting there and this maneuver helps break that crust. Hopefully things are not too rusty though.

And just for clarity's sake. What year electricals are you working with? The '73 or the '78? Or a mixture?

Paul

 

All of the electronics are from the 78, thanks, next time I am home from work I will be tearing into the ground straps!