Hi Ford Truck Forum,
I have a 78 F150 with AC, 2WD. All major AC components were removed. I was wondering if folks could help identify some wires that were snipped in the engine bay. I'm very familiar with old Ford car wiring, not necessarily truck wiring or AC wiring. I picked up the 78 2 months ago and have had to fix quite a bit...to include learning what a faulty NSS can do to a garage wall.
Anyway...I have 2 sets of wires that I dont know what they go to.

1). ...in the engine bay to a firewall plug, passenger side. 3 wires snipped about an inch outside the firewall, just below the passenger cylinder head. They go inside to the deicer (I think) and blower motor(maybe). My blower doesn't work by the way and the switch gets power. Clearly these are some part of the heater/AC system but what do they plug into in the engine bay? The wires are all painted black like every other wire in the engine bay. Do these plug into something other than AC? Do I need to run power to them?





2). ...in the engine bay, high passenger side bundled up. One is a thicker probably black and yellow wire with a female squarish connector end (gets 12V Key) and the other is a smaller yellow wire.

It's possible these connect up or at least 1 of the three from #1 go to number the square connector in #2. There might have been an engine fire at some point so I've had to trace and splice a few wires (NSS for one).

I've looked through dozens of forums and saw plenty of pictures of folks redoing their blower motors but can't seem to figure these out. I figure they might go to some of the emissions stuff that is long gone.

Ken

 

Have you tried scraping the black paint off of the wires? That might be a worthwhile effort.

 

Hey Ken, welcome! Nice truck too.
I have a '79 (which in many ways are the same as the '78) but I don't remember the two coming out of the grommet. I'll have to go look when I can, because maybe with the old A/C hose running over that area I just didn't see them.

I will say though, that "usually" a Black w/yellow wire (especially a large gauge) is usually battery power all the time. Same for many of the Yellow wires. But since the later in the seventies they got, the more wires and duplicate colors there were, I'll wait until I can review a diagram or three again. Just going by "what is common" is not always 100% going to net the right answer.

Another thing that is common with these and other vehicles, is that under hood fire or not, and removal of the A/C or not, there are often some unused connectors due to a particular truck no having had that option from the factory. Behind the instrument cluster area are usually two or three unused (but very important looking!) connectors.

Good luck. Hopefully someone with more immediate knowledge will chime in.

Paul

 

Thanks guys, I'm pretty sure one of the 3 wires coming out of the grommet is a ground wire. Tracking on the large yellow with black stripe being power, either 12V key or battery. I'll do some more digging inside the cab under the glovebox to see what color they are before going through the firewall. I assumed i'd have to pull them into the cab to splice then push back through. The square connector up top is disconnected in a photo of another vehicle I've seen.
These are tricky. From all the hundreds of wires I've tracked down from about a dozen old Fords these are perplexing me. I've checked all the wiring diagrams and just can't seen to figure out what they go to.

I've attached another picture of the truck. I've been a Mustang and Torino guy for years so they wires are generally the same color, but this truck was a mess with the crappy splices and extra junk that is no longer in use.

 

The three wires coming out the grommet are red or orange, black and black with a yellow tracer. Still not sure what they go to in the engine.

 

That blue rad support is rad!

 

Let's talk about that Mach 1 and what's on the other side of that Mach 1?

 

Do you need the bumper horns? Nice truck btw

 

Haha, the Mach1 is nice, perhaps pristine. On the other side is Stella. She's a 69 Ford Cobra. She's pretty legit and sort of rare.

I figured out 2 of the wires...blower motor. Black with yellow tracer is power. Red/orange is ground. Found a burnt ground point that matched. 3rd wire goes to the deicer. Still not sure where to hook them up. Not sure why Ford would push the blower power and ground out the firewall. Deicer is a black wire so probably ground also...again, why push to the engine?

 

Aren't the non-A/C trucks heater blower motors on the outside of the firewall? Mine's A/C so has that big tank of a box, but the non-A/C I thought had the motor facing out and the squirrel cage on the inside.
Could be wrong of course, as most other vehicles have the heater blower motor on the inside under the dash. But pickups are weird sometimes!

Paul

 

what are bumper horns? I have never heard that term. I have a single horn that works.

 

They are not green it was the picture, they are freshly re-chromed.

 

Ahhhh, bumper horns...I know them as bumper gaurds. I've looked those up. To answer the question...yes, for the right price I'd definitely be interested.

 

Bumper guards come on 2wd trucks?

 

sent you a pm