Hey guys,

I have an 85 F250 4x4 with the 6.9 l diesel.

I have been having problems with my truck not starting and the headlights flickering or not coming on.

I checked my dimmer switch today and found the wires leading to the dimmer were melted and completely corroded.

Can anyone help me with what to do next?

Is there another wiring harness or cluster I can buy as there is a connector that splits from the dimmer switch that leads to the back of the truck? I am guessing to the brake lights.

I cannot see where these wires connect as the run up through the sidewall.

Anyone know what may have caused this?

Thank you in advance for your help.

 

You need to find and replace any melted or corroded wires. Sounds like there's a short in the headlight wiring. This would be a good time to do the headlight relay project. I'm sure a search will turn up what you need to know for that.

If you've upgraded the headlight bulbs, they may be drawing more current than the original wiring was designed to carry.

There's a self-resetting circuit breaker in the headlight switch. Some of the symptoms you're seeing could be from the circuit breaker opening up when a wire is shorted out.

Probably should start by getting a wiring diagram for you truck.

 

This is not unusual for a older truck with the dimmer switch in the floor. It leads a rough life down there, with all the water and dirt. Just snip the wires off and replace the connector. I am not sure if you can get a new connector with a pigtail for it, but if you have to, you can put separate slide on crimp connectors on it and slide them on a new switch. I will look around and see if they sell a pigtail.

 

autozone sells this one for a 81. I bet they have on for yours too if it's different, it's probably the same. Part number 411.

 

Apply liberal amounts of dielectric grease to the connecter (squeeze it in to the slots for the terminals) when you install it. Corroded connections will cause overheating and it's very likely that's what happened, corroded connections lead to heat, lead to resistance lead to more heat lead to melted wires.
The dielectric grease will help prevent that in the future, but installing relays for the headlights feeding off the hot side of the starter solenoid is a really good thing to do.

 

Thank you. Referring to the relays for the headlights. I do not have that much experience with wiring. Should I splice the relay or should I run it straight from the fuse box?

Thank you again.

 

Just order the headlight relay kit from LMC truck. You can't buy the stuff for what they want for it, and it just plugs right in.

 

Dave,

Forgive my novice, so, I have a few questions:
1- does the relay include a connection to the dimmer switch also
2- does this relay include the wiring that leads to the brake light connector
3- when you say plugs right in, does that mean plugs into the fuse box and headlight switch

Thank you,

 

One other question, what do i do with the existing wires if I use the relay from LMC?

Do I cut and tape them? Remove them from the fuse box altogether?

 

There are dozens of threads on this.
Check the stickies.

It plugs into the right side headlamp socket and connects to the hot terminal of the fender mounted starter solenoid.

The harness then runs across the radiator support and plugs into the drivers side headlamp.
It includes separate body grounds for each light too.

Using the headlamp relay harness takes the filament load off the switch and energizes the headlights using a pair of relays.
This keeps the wires in the switch from carrying too much current and overheating.

As has been said, everything is 'plug 'n play', there is no cutting or splicing of wires to install these kits.

 

I know what you are thinking. No, it's not going to replace the bad wiring and connector you have, you need to fix them no matter what you do, the relay kits do not include that wiring.

The relay kit just takes the original signals from the original wires that went to the headlights, and runs them to the relays. The relays then transfer the power to run the headlights directly from the battery. So your original headlight wiring just triggers the relays, and does not run the headlights. So you do need to get your headlight wiring fixed like I mentioned.

 

Thank you very much. Now I am crystal clear. Will report back when complete.

Thanks again