So a week ago coming back to work during lunch my horns all by themselves started going off. Truck is a 77 F150 SB 4x4. So I just popped the hood in the parking lot and pulled the wires off at the horns.

A couple of days later I went to use the truck and it turned over really slow but it started.

Not sure if it’s related but when it started getting dark out I turned on the lights and no dash lights! Headlights, running lights, brake lights, signals work (even the turn indicators in the dash work), dome lights work and even the ash tray light works but no dash lights, or radio light or the gear selector light.

So I was gone for 6 days and went to go work on the truck. Battery was completely dead. So put it on the charger and tried working on the horns first. I have a spare horn relay (used one) and changed it out but as soon as I go to plug a horn in it wants to go off still! So two bad horn relays? Or is it something else I’m missing? The steering wheel is an aftermarket Grant that I put in 5 years ago and never had a problem with it/the horns at all. I replaced the crappy No name wheel that was in the truck when I got it originally. So I removed the horn switch from the wheel thinking a wire got pinched some how but all looks good. Even with the switch off the wheel the horns still want to go off.

The dash lights? I replaced the fuse and nothing still. So thinking it’s the headlight switch itself?

I don’t think the two are related. Never had a problem with any of the stuff before. All wiring is original and not cut or spliced or hacked up at all.

Someone point me in the right direction please!

Thanks for the help in advanced!

Later, Frank

 

You said you pulled the wire off the switch I am guessing up at the wheel horn button?
Dont you ground that wire to make the horns work?
If so that wire to the relay from wheel button could be shorting to ground and make it blow.

To see if that is the case disconnect that wire at the relay, hook the horns back up and see if they blow.
If they don't then that wire from relay to button is shorted to ground some where.

Because the relay was still pulled in is why the battery went dead.

Now I don't know your year trucks but I think the 80's with speed control used a horn relay and think the lights went to it also? Get the horn fixed then we can look into dash lights.
Dave ----

 

Got a manual with wiring diagrams?

The horns turn on when they get grounded out and I'm pretty sure they're on their own fuse because of that. It's happened to me twice, on 2 different vehicles, and it's been the horn wire in the column both times. Both were tilt columns and the horn wire was worn through The lighting is probably a dirty or dead light switch, all the things that aren't working have dimming capability. I've disassembled the switches before and cleaned the internal contacts, they can get oxidized over time.

Original wiring in a 40+ year old vehicle isn't always a great thing, depending on the environments it's seen.

 

I’ve got the complete shop manuals. If I have to start tracing I will. Right now I’m thinking it’s the wire in the column.

Wiring is in good shape. Not brittle etc…the wiring isn’t like in a vehicle from Arizona and it’s just baked hard.

On the lights I think it’s the dimmer switch in the headlight switch assembly. I’ll pull it out and clean the contacts etc…if still a no go I’m ordering a new switch assembly.

Keep ya posted.

 

1977 ... Grant wheel and adapter? Before pulling the center cap that relaxes the spring under it, unhook the battery. I suspect the horns going loud suddenly has to do with the ground ring that cap twists onto. Like said above, pulling horn wires under the hood just quietened the horns, but the horn relay was still pulling.

Dash lights could be just a dirty wiper or ring it slides on on the headlight switch.

 

Well I tried an old spare headlight switch and just put a brand new headlight switch in from Napa. Still no dash lights!

I replaced the fuse in the fuse block and even checked both sides of the fuse and have voltage going thru the fuse block. So it’s not a fuse or anything there.

So no dash lights, heater control light or the radio light. Everything else works. The headlight switch when fully rotated turns on the dome and courtesy lights, headlights, running lights, turn signal indicators work and the high beam indicator works as well. Just no dash lights.

I’m stumped as to where to look next to try and fix the dash lights.

Horn isn’t on my list yet. Dash lights are the priority.

Any suggestions.

Thanks, Frank

 

I did put in LED light bulbs in the dash like 4 years ago with no issues along with the heater control light and the gear selector indicator light.

The light bulb for the wiper/headlight switch is still a standard bulb as well as the bulb in the radio. That way I can dim the lights which I don’t do anyways. I have a hard time believing the led bulbs messes something up.

 

You could pull the cluster (carefully they are often brittle) and check and clean the printed circuit on the back. Use a pencil eraser to scrub the contacts for the bulb holders.
Also, check where the harness plug goes. On mine the copper strands had separated from the backing. I was able to use UV activated super glue to get them attached again. (4 1/2 years and still working)

Then trace were the light circuit goes to the plug and use a 9 volt battery and some test leads to see if you get light.

 

I’ve pulled the cluster before prior to painting the body. So I know they are brittle. I have a spare cluster and can look at that also. I’ll do that this weekend.

Thanks, Frank