Wiring harness interchangeability
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Joined: Jan 2012
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Wiring harness interchangeability
I have a '78 F250 4x4 with a 400 engine. My wiring harness from the dist to the ign module area & also the wiring harness that goes to the ignition module have been hacked, causing the dist to sometimes not get power. I plan to go to the wrecking yard to see if I can find some in better condition. My question is what years out of the 73-79 era trucks would be interchangable? Would it be 77-79? just 78? Or 78-79. I read somewhere that the '79 harness is diff. Also would it be the same v8 vs 6cyl? Thanks in advance.
MSEE
Joined: Apr 2004
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From: Austin, TX
The circuits themselves (in terms of what's connected to what) should be the same between 76 and 79, but I can't promise that they're not wrapped differently, or things branch off differently. It wouldn't surprise me if the 6-cylinder vs 8-cylinder harness is different since the length out to the distributor is different for the 6-cyilinder (it's low and on the driver side vs. up top in the front center). It also seems like there was an ignition switch change in that period, which would mean different pigtail and therefore different harness.
Mike or ND can say for sure.
Mike or ND can say for sure.
Freshman User
Joined: Dec 2006
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wiring
I replaced a behind the dash wiring harness in my 75 f100 302 - c4. Though I had an automatic I ended up getting a harness in great condition from a 76 with a standard transmission. I ended up changing out guages to warning lights and ignition switch. Connection plugs were different. Also I straight wire the back up lights. I didn't get the module wiring because I have msd. In my opinion if you go with a 79 ford you'll probably be upgrading as key and seat buzzer along with other options especiallly the intermitten wiper switch hook up. Hope this helps.
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Ok. Sounds like I need to look for a 78 with 351m/400 only then. Dang. I know the 77's have a diff ign switch, but didn't know if that effected what I need or not? I plan to swap the dist wires out, they just plug in with two plastic connectors. Then I'd cut the wires from a donor truck truck close to the firewall for the ign module & solder them to my existing. My ign module has no connectors or anything, just spliced together. My guess is that some idiot was in a hurry pulling the engine out at sometime & just cut the wires instead if disscinnecting them. 
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