Engine wire harness question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Jaysonb · 04-05-2016, 05:44 PM

My truck is a 80 stepside that had a straight 6 in it. I put a 400 in it, and I have a nice engine harness out of a 78. I notice there is a few more wires in the 80 harness, like a hook up for an oil pressure switch for the choke, but there is at least 1 extra power wire that goes to the starter. The 78 harness is nice, and all the wires are the right length. Any one know if it will work?

**MikeB** · 04-05-2016, 06:34 PM

Last year I replaced the 250 six in my 82 C10 with a 350. You're lucky to have a V-8 harness, because I had to lengthen and shorten several wires on mine. Your V-8 harness should be very close to working. The choke wire runs through an oil pressure switch to keep the choke from getting 12v (and opening) unless the engine is running. If your 1980 harness doesn't have that wire, then just find a 12 volt IGN source for the choke wire. You might have a spare terminal on your fuse block that's hot when the ignition is on.

I have installed and modified several Chevy engine wiring harnesses over the years, but could not determine why my 82 seemed to have more 12 volt "feed" wires than usual. Two wires running from starter BAT terminal to the firewall feed-through block -- one through a terminal block that feeds alternator "source" terminal. Seems like it's the old adage of "reaching over your shoulder to scratch your butt", but I'm sure there was a method to GM's madness. Anyway, I simply connected the wires like they were shown in the 1982 wiring diagram. I ended up with a total of three heavy gauge wires on the starter BAT terminal plus the battery cable. My 1969 C10 was SO much much simpler.

If you could find a 1980 wiring diagram for a V-8 it might help. Also, American Autowire makes a "Factory Fit" engine harness for my truck, but I'm not sure if one is available for your 1980.

Let me know if you have more questions. Maybe I can help.

Jaysonb · 04-05-2016, 06:46 PM

Thanks. The 78 harness seems to have everything I need, there was just more wires on the 80 harness. I might just pull the fuse box and dash wiring out of the 78, then everything should work. Alot of extra work though.

**MikeB** · 04-05-2016, 07:04 PM

These drawings might help:

http://www.americanautowire.com/PDFL...20IN%200.0.pdf

http://www.americanautowire.com/PDFL...20IN%200.0.pdf

Gotta love AAW's detailed instructions and drawings!

04-05-2016, 05:44 PM	#1
Jaysonb Registered User Join Date: May 2009 Location: Good Thunder Mn. Posts: 955	Engine wire harness question My truck is a 80 stepside that had a straight 6 in it. I put a 400 in it, and I have a nice engine harness out of a 78. I notice there is a few more wires in the 80 harness, like a hook up for an oil pressure switch for the choke, but there is at least 1 extra power wire that goes to the starter. The 78 harness is nice, and all the wires are the right length. Any one know if it will work?

04-05-2016, 06:34 PM	#2
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,484	Re: Engine wire harness question Last year I replaced the 250 six in my 82 C10 with a 350. You're lucky to have a V-8 harness, because I had to lengthen and shorten several wires on mine. Your V-8 harness should be very close to working. The choke wire runs through an oil pressure switch to keep the choke from getting 12v (and opening) unless the engine is running. If your 1980 harness doesn't have that wire, then just find a 12 volt IGN source for the choke wire. You might have a spare terminal on your fuse block that's hot when the ignition is on. I have installed and modified several Chevy engine wiring harnesses over the years, but could not determine why my 82 seemed to have more 12 volt "feed" wires than usual. Two wires running from starter BAT terminal to the firewall feed-through block -- one through a terminal block that feeds alternator "source" terminal. Seems like it's the old adage of "reaching over your shoulder to scratch your butt", but I'm sure there was a method to GM's madness. Anyway, I simply connected the wires like they were shown in the 1982 wiring diagram. I ended up with a total of three heavy gauge wires on the starter BAT terminal plus the battery cable. My 1969 C10 was SO much much simpler. If you could find a 1980 wiring diagram for a V-8 it might help. Also, American Autowire makes a "Factory Fit" engine harness for my truck, but I'm not sure if one is available for your 1980. Let me know if you have more questions. Maybe I can help. __________________ Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then!

04-05-2016, 06:46 PM	#3
Jaysonb Registered User Join Date: May 2009 Location: Good Thunder Mn. Posts: 955	Re: Engine wire harness question Thanks. The 78 harness seems to have everything I need, there was just more wires on the 80 harness. I might just pull the fuse box and dash wiring out of the 78, then everything should work. Alot of extra work though.

04-05-2016, 07:04 PM	#4
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,484	Re: Engine wire harness question These drawings might help: http://www.americanautowire.com/PDFL...20IN%200.0.pdf http://www.americanautowire.com/PDFL...20IN%200.0.pdf Gotta love AAW's detailed instructions and drawings! __________________ Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then!

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