It was a nice day in sunny Florida when my stepdaughter called looking for a ride to work, about 40 mins from her home. I jumped on the Interstate put up all the glass, turned on A/C and started a nice chat with one of the children I don't see much anymore. Most things I smell don't get much attention in a 35+ year old truck but this was different, smelled like plastic so it got my attention quick. I have had my dash pulled down completely to replace all the lighting and replace what the PO hacked when installing his tunes. I remember the connector on the fan switch being a bit loose and sure enough I got a wake up call when I grabbed it (melting plastic sticks to skin well). Thanks for reading the short story!
It's a 77.5 F250 w/factory installed A/C , any idea where I can get a new switch / connector w/pigtail? I'm not ready to loose my truck to fire, must be a sick feeling to standby and watch your ride go up over such little stuff.

 

Stinky7-11 sorry to hear about your almost big issue, glad you caught it. I can ck my local JY for you, but can't get there till Monday.....

 

That would be great! Thank you

 

Do you need the connector for the fan speed switch, or the selector switch?

 

I need both if possible but the connector most!
It has four connections three vertical one horizontal.
I will post photo tomorrow

 

Sorry, I meant do you need the connector that goes to the back of the fan speed switch, or the connector that goes to the selector switch?

The former is easy to get new, not sure about the latter. Will wait for your photo to be sure.

 

From the looks of it, my donor truck nearly went through the same thing. When I tore the dash down, the blower switch was showing signs of beggining to melt and the insulation on the red w/black trace wire was litterally melted to the point of exposing the wire conductor.
This accessory harness is not available, I looked, no one has one NOS.
I found a supplier that could get me the correct color coded wire in bulk lengths. I also found the correct factory terminal ends so I rebuilt the harness that I had.

 

Stinky, when you do the repairs you might want to check your blower motor. I strongly suspect this is what caused my wiring to melt, altough I can't prove it because this was a donor truck and I never really drove it and the A/C didn't work anyway.
What I suspect happened was the blower motor was on it's way out and "dragging" causing it to draw more amperage than normal but not enough to blow the fuse. Drawing high amps over an extended period of time allowed the wiring to overheat, melting the plug and wiring.
I was planning on replacing the blower motor anyway but I checked the old motor on the bench and it would only turn slowly even though it was connected directly to a 12V source. I also had a burned out blower resistor.

 

I also want to mention that the wiring and switches in the blower motor and headlight circuits on early Fords is typically undersized. It's not uncommon to pull apart the speed or selector switch and find burnt wiring or switch contacts. The blower motor is also highly inductive and the switches cannot typically handle the voltage arc that shows up when you shut off the fan. This is exacerbated by heavy current pulled by a failing blower motor as Mike describes.

 

another problem is that older vehicles didn't fuse a lot of circuits, or they ran several accessories off one circuit with a large fuse, so that a single accessory can pull well over what it should without tripping the fuse if the other accessories aren't on.

 

On my wire harness, the red wire that melted was 14 ga. when I ordered new wire I ordered 12 ga. and replaced the switch along with the blower motor.

 

Thank you all, here are photos, I got the truck from Arizona so no rust but plenty of heat & dust! I should have purchased stock in Weatherpack as I have used them to replace many orig electrical conectors and light sockets. When I read threads about sheet metal replacement I sit back and realize how lucky I am with this truck, this is my first with ZERO rust! But!!! what I saved in metal work I spent replacing rubber and electrical items ha ha.
I will check my blower motor, thanks for the heads up, if anyone can point me towards the connector and switch that would be awesome.

 

The switch is easy, Motorcraft YH-2. The socket is another story. You have the 73-77 socket. This is different from the 78-79. When I was looking for a replacement for mine ('73) I ran into the same problem. There are plenty of the late model sockets around, easy to get. I saw the exact same socket priced from $2.99 to $36.95 (!). I also saw a lot of these listed as fitting the '73-'77, they DON'T. I never could find the correct socket. Fortunately, at the time I must have been having a brain freeze, this plug is part of the main harness, I was looking at my donor's plug, all melted. Then it dawned on me, look at the plug in the Pumpkin's harness, THAT'S the one I want to use. It was fine so I dodged a bullet on that one.

 

I have a pile of harnesses...I'll check tomorrow and see what I have.

 

Here's the 78-79 socket that's easy to get.