3G Swap, No Start

[FordDZLMan9191]

I bought an 86 F-250 6.9 that supposedly ran great. Well, turns out it needs a lot of work but the original alternator was shot and while looking for a replacement, I found some info about swapping a 90s 3G alternator on the truck. So I went out picked up a 130 amp unit from a 91 Mercury Sable with the 3.8L. After looking up and printing out wiring diagrams for both my truck and the car and thinking I had it wired correctly, I have no power to the truck at all. I wasn't able to get the harness from the sable or one from a crown vic like the info I found said. Can someone give me some good detailed info about this so I can get my truck running? Thanks.

 

[Optikalillushun]

Then how did u wire it up. Pics or a detailed explaination. I dont see how u can wire it up without the plug.

 

[FordDZLMan9191]

The alternator I got still had the plug on it but the wires were cut on it. The info I read said to get the entire wiring harness from the car or one from a crown vic would work too. None of the yards in my area had the harness apparently. Doesn't make sense to me why not, but I couldn't get it.

I spliced my trucks wires to the corresponding wires on the alternator. New big wire from stud to solenoid on fender, yellow/white to solenoid on fender as well, green/red to green/red and the white/black to the stator. My friends dad is a mechanic and was helping me look over the wiring diagrams and thinks this should be right going by the diagrams but hasn't looked at it in the truck yet.

 

[Optikalillushun]

The alternator I got still had the plug on it but the wires were cut on it. The info I read said to get the entire wiring harness from the car or one from a crown vic would work too. None of the yards in my area had the harness apparently. Doesn't make sense to me why not, but I couldn't get it.

I spliced my trucks wires to the corresponding wires on the alternator. New big wire from stud to solenoid on fender, yellow/white to solenoid on fender as well, green/red to green/red and the white/black to the stator. My friends dad is a mechanic and was helping me look over the wiring diagrams and thinks this should be right going by the diagrams but hasn't looked at it in the truck yet.

Ok makes sense now, i was under the impression u didnt have the plug. U dont neccessarly need the whole harness just the plug and about 6" of wiring. First things first if u havent already i would add a fuse to that power wire. I like mega-fuses they have a nice rubber/plastic holder:

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As for the wiring, lets see what ya got...seems u wiring it up correctly but i ran the yellow/white to the power lug on the back instead of to the solenoid. Since it seems its wiring right i would take a look into the fender solenoid. make sure u are getting 12v from the battery to the inner large post. Is everything hooked back up correctly? I left the small wire going to the starter off the solenoid and i coulda kicked my own ass when i realized what i forgot.

 

[FordDZLMan9191]

I'll try to get some decent pics. I wasn't sure how much of the original harness needed to be left so there's still most of it there.

When you say you have your yellow/white to the "power lug on the back", are you meaning the stud on the alternator or what?

 

[Optikalillushun]

yes on the stud at the alternator. Really makes no difference tho.

 

[FordDZLMan9191]

Wasn't sure what to get a pic of so this is what I took. My connections are on the backside of the alternator(toward engine). Don't know if it'll help you much...

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The blue tap splice on the yellow is the other yellow wire that came from my original voltage regulator with the other yellow wire and dead ended. Wasn't sure if it needed to be kept or not.

 

[Optikalillushun]

Dont take what im gunna say as being an ******* but scotch-locks/wire taps are complete garbage and make a wiring job look **** poor. More so being on a diesel that has a lot of vibrations they will eventually fail. Please re-do the wiring, here is how i did mine:

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Only took me about 30 minutes and some materials. Plus doing it as its own harness allows for easier dianostic work later down the road. My opinion is to unplug the connector near the fender that houses the green/red wire (which is part of the regulator wiring and also has the tach sendor) and plug from the alternaotr and make it its own:

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[riotwarrior]

I just did a 3G on my Bronco gasser...love it, one thing I noticed, your Alt is not clocked so that the plugs and stud face out towards the passenger fender. I strongly suggest that you take it out and reclock it, this allows wire access and easy checking of wires and trouble shooting. See Optikals leads on his setup...that's the best way. Plus it ensures that the main power wire has a clear line to the relay.

Also as stated a good idea is a positive lead fuse, I have a 250 Amp alternator so I used a 200 amp fuse.

One more thing, I'll try getting some pics tomorrow, I run a ground wire directly from the battery to one of the main mounting bolts on the alternator as well. Just me being over kill/OCD about electrical isses... what else is new right?

 

[FordDZLMan9191]

Got it figured out. Ended up being I missed a wire. Just gotta go through and rewire it to look neater and fuse it. Got 14.32-ish volts at idle.

 

[KyleQ]

Yeah, I was going to say if you have zero power you don't have something hooked up - the alternator is there to charge the battery, it doesn't interrupt anything.