I’ve been looking all through the first reads and other posts in case my question has been asked before but here I am.

I have 77 F250 4x4 351m Manual that has a cut up and spliced together wiring harness.

I have a 78 F150 2wd Auto “parts” truck that I’m taking pieces from that I can. I have pulled the entire wiring harness from the 78 because it is pristine and complete to use in the 77.

My question is, when looking more closely at the 77 engine bay I’m seeing some differences in the alternator and voltage regulator components. The 78 has a 3 wire alternator and square shaped voltage regulator while the 77 has a 1 wire alternator and some kind of bulb shaped voltage regulator (similar in looks to a hazard flasher bulb). I’m thinking that at some point in the past the previous owner put in the 1 wire alternator and made some other alterations. If I put in the “new” harness from the 78 will I need to change the alternator and voltage regulator back to a more stock configuration? Both trucks have the two plug ignition module. I’m also pretty sure I’ll need to swap the ignition switch housing/plug as the 77/78 are a different plug style on the back of the switch. Am I overlooking any other problem areas?

Thanks for the help!
straycat

 

I am not up on the 73 to 79 trucks like the 80 to 86 trucks but do both of your trucks use gauges or lights for the dash?
I think dual tanks are an add on for your years unlike the 80's so that should not be a thing.
How is AC run on your trucks, its an add on to the 80's

As fore the ALT you can either swap back to the factory so you dont have to cut the harness for the 1 wire and be able to get parts at most any store.
I am not a fan of the 1 wire. I have seen some not keep the battery charged because it senses output at the ALT not the battery.
You have a lot of draw on the battery but the ALT sees no load or draw at the ALT so the battery goes dead.
If you look at how the factory senses battery volts it picks it up with a splice on the wire feeding the truck not at the ALT.

Dose the parts truck have a ALT & Reg you can use?
Dave ----

 

Thanks for the reply!

Yes - both trucks have gauges so I think I'll be good there. The 77 only has the cab tank - I'd have to double check if the 78 has dual tanks or just a single. The 78 has AC the 77 is non-AC. The parts truck does have an ALT & Regulator that I can use so I was going to swap those out as well.

The 78 had a lot more options than the 77 (Cruise and Factory AC) but I was thinking that I'd just leave those connectors unplugged and hook up everything else.

Straycat