Hey all, I think this is my first post. 84 F150 4x4. Let my buddy borrow the truck, came back with a half tank of gas, no lights, and a bleeding wheel cylinder. Grr. Anyway, got the brakes in order, now to tackle the electrical.

Current status:
Brake lights work.
Turn signals/hazards work.
Headlights DO not work, nor do the side markers, "parking lights" or dome light.
Threw a new switch on, no dice. Oh well, it's cheap, I shoulda checked more things first.

Probed out the switch harness with the multimeter, no voltage on any of the feeds that (according to the Haynes anyway) should be hot all the time going into the switch. Fuses are all fine, fusible links all look to be in order.

Lucky for me, this is the epitome of a beater truck, so if I get too pissed off at it, I'll just run some relays and new switches all around. Obviously, I'd rather just figure out wtf is going on with it first. Thanks in advance, I'm going to go back to digging through old posts and drinking beer and staring at this rat's nest of 23-year-old wiring.

 

Update: No voltage at the fuse panel on the courtsey or tail light fuses. Again, the fusible links (i'm seeing 3?) all look fine. I ran a jumper to the back of the switch and was able to get power to the courtesy/marker lights no problem, so barring someone coming up with an amazing solution, I think I'm just gonna run a maxifused heavy gauge wire into the cab, split it off and feed the lines on the switch looking for 12v and call it day.

 

You are all around it. The wire for the headlights starts out at the starter relay power area where the fusible links are located , and runs right into the headlight switch. From memory, it's a black/orange.

 

Any idea what route it generally takes? It gets lost in the looms pretty quick. Even if that one wire was shorted somehow, it wouldn't affect the courtsey/dome/marker lights though right (since they're seperately fused). Just trying to figure out what would take out EVERY single hot feed to that switch. (and not any of the fuses or fusibles)

 

Fusible links can appear to be ok even when burned out because of the insulation used on them. They are burn resistant. You need to test headlight wiring from source to switch. There should be a connector under the dash that can be unhooked and tested. I don't have diagram, but you may be able to determine which wire it is as it is probably a large one.

 

Going from memory here, but that fusible link wire is only for the marker lights I believe (according to the schematic)...there should be 3 hot feeds, headlights, markers, and interior....all 3 feeds at the switch harness are 0V though...if the fusible link was dead, (by my reasoning anyway) I should still have interior lights and headlights, which is what's really hurting my brain on this.

 

When you pull sw out to first position, that is marker(parking)lights. Next position is headlights. Same hot wire could feed the switch. I'm guessing here as I don't have schematic.

 

No, he's right, there are seperate feeds to the headlight switch.

Here's a lousy diagram.
http://www.autozone.com/images/cds/g...3d800ce991.gif

The tan/white feeds the marker lights. Check for power on the fuse for the marker lights. One side of the fuse socket should have power. I believe that part of the fuse box get's it's power from the yellow wire.

 

Yep, that's the exact diagram I'm going off on in the Haynes manual. Pulled the fuse, either side of the fuse plug has no power at all, fuse itself is fine. Like I said, I have 0 idea what in the hell would cause all 3 feeds to go dead. Same goes for the other fused link (marker, interior).

I was hoping there was some amazing common issue with these trucks, but since I havne't seen it, and/or it hasn't turned up yet, I think I'll leave it a mystery for the ages and just provide new feeds. I can't pull a good enough diagram to figure out what wire provides the feed to the fuse block, running new fused hot feeds to that switch is gonna take much less time than figuring out wtf is actually going on, as much as I'd really like to know at this point.

 

My Haynes manual has a very good factory diagram, much better than the one in the link. If you have it, I am looking at "power distribution wiring diagram, 1984-1986".

Surprisingly, this diagram shows the tan/white fed directly off the black/orange, unfused. That is a typo, so much for the good diagram.

Anyway, there are two main power feeds. The black/orange that feeds the headlight switch, and the yellow wire which feeds the ignition switch, and the hot all the time part of the fuse box. The yellow is fed by a darkgreen fusible link, and the black/orange is fed by a orange fusible link.

If you are feed power directly to the power wires, I think I would unwrap the harness over at the solenoid, and jump the wires downstream to see if you can get power to the lights and the fuse box.

 

Actually, I had a black/orange 12gauge feeding the switch, and a 18ga white/tan. Replaced both feeds with new 10ga/14g appropriately fused runs from the solenoid, and everything (except the dome light) works fine. Good enough for me, I'm going to button it back up tomorrow. Did run into an oddball issue with me not being able to read a schematic, and putting 12v constant to the blue/red line causing the markers to be on (dim) at all times. Re-connected it properly, and it's all kosher now.