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Alright all, this is a 78 f150 4x4 with a 4 spd that came with a 351m. We sold the motor (kept the 4 speed) and are installing a freshly rebuilt 429. Waiting on the heads (🤬 that were supposed to be done weeks ago. Anyway, it’s a project truck with my son. So junior took the old engine out and now we are trying to put things back together but I am lost on where wires go…. Not sure if there was a harness on the 351 that he sold with that motor. Please see pics. Any help on what goes to what would be greatly appreciated!! I should add we did a cab swap. But the harnesses looked the same so this harnesses is from this cab. Only difference was this cab had AC, which we deleted.
while I’m asking. Is there one wire I could run to hot to simply check internal wiring?? Lights, dash, etc……. ? Wires coming out of firewall mid/passenger side. I see the plug that goes to the blower motor. Main harness coming out of drivers side cab. Found a couple to hook together Additional wires from drivers side We did get updated dizzy from Scotty J the mad porter.
You have a shop manual with wire schematics maybe? Might be clearer than a picture posted here would be? You have wires for lights, ignition, instruments, horns, charging, power distribution, washer motor, etc. Labels would be great, but wire colors and locations and plug configurations ... & memory ... will have to do.
You should of kept the old none a/c cab harness and transferred it over. 99% sure they are/is a difference in the 2, but too late now? IMO the easiest and most reliable way to go it to get a NEW repop harness all together. As in for the whole truck, like from Painless, American Auto Wire or Classic Industries.
Yes I know it is a lot of $ up front, but the benefits of NEW wiring is well NEW WIRING, blade fuses and it is all marked for install, which is a good thing. And all said and done you should not ever have any wiring issues on down the road.
There is a short eng harness that goes down the dvr side, between the carb and valve cover for the eng temp, and oil pressure sending units. Did the new 429 come with anything wiring wise? In your pic the big long one on the coil tower (square 4 pin) is for the front lights. Should be another on on the pass side. Should be the rest of the harness going the core support. The odd shaped 2 pin is for the w/s washer pump.
You should of kept the old none a/c cab harness and transferred it over. 99% sure they are/is a difference in the 2, but too late now? IMO the easiest and most reliable way to go it to get a NEW repop harness all together. As in for the whole truck, like from Painless, American Auto Wire or Classic Industries.
Yes I know it is a lot of $ up front, but the benefits of NEW wiring is well NEW WIRING, blade fuses and it is all marked for install, which is a good thing. And all said and done you should not ever have any wiring issues on down the road.
There is a short eng harness that goes down the dvr side, between the carb and valve cover for the eng temp, and oil pressure sending units. Did the new 429 come with anything wiring wise? In your pic the big long one on the coil tower (square 4 pin) is for the front lights. Should be another on on the pass side. Should be the rest of the harness going the core support. The odd shaped 2 pin is for the w/s washer pump.
The Chilton/Hayes manual version.
I actually kept the original harness which is laying in the box. Problem is he chewed it up cutting away to remove it. That’s my fault though as I told him go nuts, rip it out as my plan was to use the one from the donor cab, I know one set of wires (I don’t have) go from the voltage regulator to the distributor. Long ones on each side make sense…. Core support. Oddball two plug for washer tank makes sense. There’s like 3 other plugs coming out of the firewall. Any ideas what those are for?
Lessons learned that are painful or expansive tend to stick with you the rest of your life. Lol I think the harness from the a/c cab could be MADE to work, but pretty sure there are some differences. Time to get the multimeter out and go to town on it. If it turns into a nightmare, I think a new repop harness is the faster and less headache way to go. The differences are especially the environmental control part. A a/c harness has more wiring to go to more components like sensor, vacuum valves. I know 2 elec conn that are on the dvr side on the mass bundle are for the electronic ignition "brain" box. I seem to remember a couple are not used.
go to the link below, scroll down to 1978. All connectors are shown along the bottom of each page, some with location...should be able to figure it all out from there...
Were both the original truck and the new cab from '78 trucks? If not, and it's not a '79 (the only other year that's close in wiring) then the wire harnesses might actually be quite different. Especially with the design of plugs/connectors and such.
The wire colors will still mean the same thing in about 80% of the cases, but even the same color wires might not be routed the same between the two.
Anyway, hopefully they're both '78's and you can get through this.
The wires you mentioned just above, going from the voltage regulator to the distributor, doesn't make sense to me. The distributor of a '78 has three wires and they all go to the ICM (or ignition control module) on the driver's fender. Shown in one of your previous pics (front clip standing on end maybe?). Oh, maybe that's what you're calling the voltage regulator? Ahh, that would make sense. If so, then nope, that's the Ford Dura Spark ignition module. And the wires going to that would make sense. Should be a blue colored strain relief (commonly referred to as a "grommet") where the wires come out of the module.
Are you planning to keep the stock ignition system?
Were both the original truck and the new cab from '78 trucks? If not, and it's not a '79 (the only other year that's close in wiring) then the wire harnesses might actually be quite different. Especially with the design of plugs/connectors and such.
The wire colors will still mean the same thing in about 80% of the cases, but even the same color wires might not be routed the same between the two.
Anyway, hopefully they're both '78's and you can get through this.
The wires you mentioned just above, going from the voltage regulator to the distributor, doesn't make sense to me. The distributor of a '78 has three wires and they all go to the ICM (or ignition control module) on the driver's fender. Shown in one of your previous pics (front clip standing on end maybe?). Oh, maybe that's what you're calling the voltage regulator? Ahh, that would make sense. If so, then nope, that's the Ford Dura Spark ignition module. And the wires going to that would make sense. Should be a blue colored strain relief (commonly referred to as a "grommet") where the wires come out of the module.
Are you planning to keep the stock ignition system?
Paul
i purchased an upgraded distributor from Scotty the mad porter. Was under the impression the rest of the stock ignition would work well.
come to think of it, I had it backwards. The harness in this truck is from the original cab, as original owner had plow wires spliced in that I had to remove yesterday.
my apologies I thought that was the voltage regulator but yes that would be the ignition module. I took a few more pics of the original harness that came with the donor cab…. Pretty cut up but I think I can follow most of it. Maybe this will help provide some additional direction. Still not sure what the extra plugs exiting drivers side firewall on my first set of pics is for though…. On the ignition module there are two plugs. If one goes to distributor wouldn’t the other one attach to the main harness coming out of the cab? In case you can’t tell, automotive electrical is not my forte but am grateful for the help! Old main harness - cut into pieces from previous owner but glad he tossed it inside the cab for me This appears to be the cut portion at the firewall near passenger side. If I’m correct this will have the plug for the blower motor, attachments to starter solenoid and go on to have to have the plug for the headlights Not sure what that one heavy orange wire goes to….. I think (?) this runs from the solenoid then over to the coil and distributor plug? Not sure what this was for
I’ll have to wait till I get back to my computer with a bigger screen to point some things out. But one of the things that always causes trouble when discovering new things on a vehicle’s wiring harness, is the fact that many trucks did actually have extra connectors that were not used.
That may be part of what you’re running into at least.
Unused connectors would’ve been for other options that a particular truck did not have. They learned long ago that creating completely different harnesses for every variable of options, was not very efficient. So there may have only been one, or perhaps two main wiring harnesses installed in these trucks at the factory.
They would’ve been the same whether the truck was completely devoid of options, or had everything and the kitchen sink.
I’m not exactly sure about the big orange wire.
In my experience, the only two orange wires on our trucks were the one for the field current of the voltage regulator, and one for the main fuel tank sending unit.
Yours definitely has a fusible link end there at the ring terminal.
I can’t tell the size exactly, but that fusible link does make it look like it should have been connected to the battery side of the starter relay/solenoid.
Don’t remember fusible links in the alternator field wire, and it would have normally been molded into a wire strain relief with the white and black and orange wires all together.
The diagrams posted above should show us any additional orange wires. I’m just not remembering what they are for.
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that were supposed to be done weeks ago. Anyway, it’s a project truck with my son. So junior took the old engine out and now we are trying to put things back together but I am lost on where wires go…. Not sure if there was a harness on the 351 that he sold with that motor. Please see pics. Any help on what goes to what would be greatly appreciated!! I should add we did a cab swap. But the harnesses looked the same so this harnesses is from this cab. Only difference was this cab had AC, which we deleted. 
