after a long stent of bad luck my truck is finially going back together, i wont bore anyone with long details except im going late model with a standalone ecm, the shop that was helping me closed down and left everything dangling wire wise from the firewall, i have looked all over the wiring diagrams and looked at forums and found td just be easier to ask for help, im just looking for the rite wires to hook back into to power up the cab and let the ecm take care of everything else, am i looking for a single input that will run back to the switch or is this going to be a multipoint connection? i know most of the power came from the right side *where the battery solenoid and regulator was * i know the old solenoid points will give me my triggers i need for ecm control and function, or would it just be easier to run a new heavy gauge back to the fuse block and just delete all loose hanging wires, i know the answer is probably simple but im just tired of overthinking the whole mess and debacle of what has transpired without burning it al to the ground by accident, TIA for any help

 

so you have a complete wiring harness from a later model truck?

here are factory wiring diagrams for sever model years if you are going back with factory/original harness...
https://fordification.net/tech/wiring.htm

 

The part of the harness in your hand looks like it might be the original for your '75 maybe? If so, the two wires to the left with the 90 degree elbow push-on connectors appear to be for the starter relay/solenoid on the inner fender. If so, one would be a Red w/blue stripe and the other is Brown?
If so, the Red w/blue goes to the "S" terminal of the starter relay and is the one that comes from the ignition switch and energizes the relay and starter when the key is in START only.
The Brown is spliced into the Red w/green wire for the old ignition coil at a connector towards the back of the engine near the firewall. It supplements the power to the ignition system and is not strictly required for your new conversion.

And speaking of which, you will probably need to bore us with lots of other details. This was already NOT a basic do-over, but now that you've been left with half an unfinished project, it's going to need even more help that it would normally. So spew forth with some more gory details and pictures (especially pictures!) and let us have at it with you.

The larger 3-wire plug in the background of your picture is the charge wire setup for the alternator most likely. The large Black w/yellow stripe wire is the wire from the BAT terminal of the alternator.
Not sure if the one in the pic is the body side or the engine side, as I'm not intimately familiar with the '75. Or a lot of the years for that matter.
Ford did change things over those years....

And speaking of details, what year is the donor truck? Just "later model" is not going to cut it as there are almost 50 years worth of later models in that time!
Is it the whole engine and induction system? Or just the later parts put on your older engine? What engine is it? What year donor? What mixture of wires?

Oh, and the main power for your entire truck travels along a Black wire of the same gauge as the one in your picture, connected directly to the battery side of the starter relay. A fusible link is the protection provided by the factory, but when that ever blows out we sometimes replace them with an easier-to-service fuse.
But we're definitely going to need more pics.

Thanks

Paul

 

I really wish i had the time to lay down a time line and how long its taken along the way with small stories, SO i guess i will get the gore out of the way,and no its not a basic doover, and i am sure when the purists see hear this im going to catch hell which ive already had a lot, the late model is a 6.0 LS and 4l80e *pics will be posted at the bottom... i will back track to when i was a paint salesman, my background is auto collision technology specializing in refinish and metal work , i am no mechanic by no means but if its going to shine or stick im your guy, so during my sales years i met and seen a lot of *fabricators* go out on their own and fail, few i got to know well so i thought this guy i thought i knew well went out on his own*like others before him*.. in the mean time i went into the oilfield and gone and traveled a LOT and was gone, so we made a deal, rebuild my twin I beam front end of my beloved yellow truck that was handed down to me by my gramps up and running rite like he woulda wanted, so as im gone he was supposta be working and like most hard times hit him and his shop *proabally over the same deals i got into*, i got word to go get your truck *legal reasons leaving names out* has shut down and left the counrty no one can find him, finially im able to go get in snag my truck in pieces, 390 sitting in the bed no heads just a short block and full of water and no front sheet metal just a hood..mean time a real friend started doing fab work at home, we rip the rest of the twin out, decide money wise and asthetics a crown vic k member is in order, so im still left with dangling wires from the firewall,and no engine.. as a good friend he hooks me up with one of his rebuild 6 liters *ive actually seen run on the stand crank dyno around 480 power, sells the whole kit and caboodle to me buddy deal i help him paint wise he helps me fabrication wise we both walk out winners, so now i get it all set, new inner fenders, redone firewall, friend makes new bracketry for the engine and trans.. now im left with the rest and enter my issue and carnage, Gm usualy most generlly had heavy gauge wires that connected to the starter wich powered everything inside.. well ford doesnt unless im missing the point, i have the old ICM wires that comes from the passenger side, another set of identical ICM wires that come from the drivers side *all pictures below* and btw paul thank you for our input..so to power up my cab and accessories inside i have to figure out wich ones to tap into from a standalone harness without causing more damage to me and my truck that has already been done, no doner stuff just new stand alone and danglies from the firewall, btw i did identify the lights, electric choke and washer pump from the wiring diagrams on the webside, other than that this is it

what is left of the 390

right fender aprin

left fender aprin

new engine mounts

new tans mount

as looks looks today

bonus interior shot

 

Wow, what an epic battle! Totally worth it though as it was your grandpa‘s truck.
Do whatever you can to keep it in the family and running.

And yes purists will always be haters about putting a GM engine in a Ford and vice versa, but it’s hard to argue that the“LS“ family of engines are probably the best package ever designed around a V-8.
Compact, relatively light, very powerful, and even very fuel efficient in some cases (it certainly is in my case!).
Easy to package in just about any vehicle.

Don’t give GM too much credit though, for the common wire point down on the starter. It was a horrible mess after a few years in many cases.
Not every vehicle had the problems, but every one I ever worked on had oily, gunky, deteriorated and failing wires down there due to heat and petroleum exposure.
Too close to the exhaust and prone to collecting oil from leaks.
Not to mention it was awkward to do wiring work, at least from the topside. And that’s even without headers!

Ford’s idea of the separate starter relay up on the fender for use as a common wire point was actually better in my opinion. More out of harms way, easier to service, and easier to source as a common PowerPoint.
So much so that even after Ford went back to a starter with a piggyback solenoid on it, they kept the relay on the fender. As far as I know to this day…

 

And while you are at the rewiring stage, don’t also follow the traditional GM practice of putting the ground cable on the front accessory drive brackets.
Even GM doesn’t do that anymore.

Pay the extra couple of dollars and run a longer ground cable down to the engine block.
Closer to the starter is better, even to the point of using one of the starter mounting bolts as your ground point.
Personally I prefer to use some other bolt so that the ground wire isn’t needing to be messed with when just changing a starter. But a starter mounting bolt is arguably an excellent place to put the main ground cable.
Or at least a branch of it.

 

Thank you sir and yes we cannot deny the upgrade a Ls can bring and still bring 13lbs of mercury vacume even with a large cam, like i said its there now LOL, Since i first posted i done some digging and made a discovery, the wiring is Trash, I spent a hour yesterday taking it all out, and it sounded like a box of crackers in its own loom, so if it wasnt for us discussing and digging id had a real problem, so the decision is to go to painless and have them build a loom for me, Not my first idea to have done But definitely NOT disappointed by the decision LOL

 

I hear you on the old tired wires.
The wires in both my’71 and ‘79 are still in surprisingly good shape for their age. But when we were fuel injecting my friend’s 77 and he wanted to re-wire later, things did not go according to plan. All the wires were as brittle as yours sounds like. Every time we tried to move some wires the jackets broke!
Needless to say, it got a new harness at the same time.

 

Compleatly agreed, what was under the hood seemed fine, i guess what was under the dash was trashed and been in a fixed position so long they took a fixed position.. Thanks for your help Paul.. Ill keep you posted on furture progress, glad to know you are not a hater of the build lol

 

Following!