Wiring Harness Interchangability 84 Truck, 72 Engine - The 1947 - Present Chevrolet & GMC Truck Message Board Network

thefraze_1020 · 04-16-2014, 08:59 PM

A while back, I posed the question "how hard is it to put a 350 out of a 72 into an 84 that originally had a 305, mated to a Muncie 4-speed?"

I now have a new question. When I pulled the 305 a couple weeks ago, I noticed that the wiring harness wasn't in that great of shape. If I remember correctly, the engine wiring harness out of the 72 was in better shape. How easily can I swap the engine half of the wiring harness? In other words, how much different are the harnesses from a 72 and an 84?

Also, my radio/ speaker wiring was modified a bit in the cab. At this point, should I just be thinking about replacing the whole harness?

SSC's76 · 04-17-2014, 06:19 AM

There are a few differences wipers come to mind. I would repair the current harness or go painless. It would be a lot easier to repair the current harness there isn't much under the hood to worry about.

ray_mcavoy · 04-17-2014, 06:16 PM

I don't think the 72 engine harness will come any where close to working in the 84.

In addition to the wiper motor difference that SSC's76 mentioned ...

(1) The 72 engine harness uses a 10 cavity connector where it attaches to the firewall bulkhead connector. The 84 on the other hand has a considerably larger 22 cavity connector for the engine harness.

(2) The 72 engine harness does not contain any wiring for the alternator. That is all part of the headlight harness on the 72. And unless it's been modified it would be configured for an externally regulated alternator mounted on the driver side of the engine. The 84 originally used an internally regulated alternator mounted on the passenger side.

(3) Unless it's been modified, the 72 engine harness will have a resistance wire feeding the coil for the points ignition system. The 84 originally had an HEI distributor fed with a regular 12ga wire.

So like SSC's76 said, you'd be better off repairing the existing 84 engine harness. Or replace it with a new or better one if it's beyond repair.

As for the cab & under-dash wiring, all of the speaker wiring is separate from the main harness. The main harness only has 3 wires for the radio ... yellow (power), black (ground), and gray (dial light).

thefraze_1020 · 04-17-2014, 10:54 PM

I installed an AM radio in the dash tonight, and all I've got to do is wire up speakers and use butt connectors for the yellow/black/gray wires.

04-16-2014, 08:59 PM	#1
thefraze_1020 Registered User Join Date: Mar 2014 Location: Mount Vernon, WA Posts: 417	Wiring Harness Interchangability 84 Truck, 72 Engine A while back, I posed the question "how hard is it to put a 350 out of a 72 into an 84 that originally had a 305, mated to a Muncie 4-speed?" I now have a new question. When I pulled the 305 a couple weeks ago, I noticed that the wiring harness wasn't in that great of shape. If I remember correctly, the engine wiring harness out of the 72 was in better shape. How easily can I swap the engine half of the wiring harness? In other words, how much different are the harnesses from a 72 and an 84? Also, my radio/ speaker wiring was modified a bit in the cab. At this point, should I just be thinking about replacing the whole harness? __________________ Cameron 1984 Chevy C20 Custom Deluxe

04-17-2014, 06:19 AM	#2
SSC's76 No No Join Date: Jun 2005 Location: Pueblo Colorado Posts: 1,781	Re: Wiring Harness Interchangability 84 Truck, 72 Engine There are a few differences wipers come to mind. I would repair the current harness or go painless. It would be a lot easier to repair the current harness there isn't much under the hood to worry about. __________________ 1976 Custom Deluxe SWB Med FMB.3/4 Drop. Gen VI 454, Muncie HD 3 speed With Modified OE Hurst Shifter, 3.73 12 bolt, GMPP HO roller cam, Hooker headers, Performer intake with modified Q-jet, Accel distributor. Best 1/4 12.3 @108. Funnest run 19.84 @88 full 1/4 mile burn out. 1997 K1500 ext cab 5.7 stock except muffler

04-17-2014, 06:16 PM	#3
ray_mcavoy Registered User Join Date: Nov 2009 Location: Sherman, ME Posts: 2,360	Re: Wiring Harness Interchangability 84 Truck, 72 Engine I don't think the 72 engine harness will come any where close to working in the 84. In addition to the wiper motor difference that SSC's76 mentioned ... (1) The 72 engine harness uses a 10 cavity connector where it attaches to the firewall bulkhead connector. The 84 on the other hand has a considerably larger 22 cavity connector for the engine harness. (2) The 72 engine harness does not contain any wiring for the alternator. That is all part of the headlight harness on the 72. And unless it's been modified it would be configured for an externally regulated alternator mounted on the driver side of the engine. The 84 originally used an internally regulated alternator mounted on the passenger side. (3) Unless it's been modified, the 72 engine harness will have a resistance wire feeding the coil for the points ignition system. The 84 originally had an HEI distributor fed with a regular 12ga wire. So like SSC's76 said, you'd be better off repairing the existing 84 engine harness. Or replace it with a new or better one if it's beyond repair. As for the cab & under-dash wiring, all of the speaker wiring is separate from the main harness. The main harness only has 3 wires for the radio ... yellow (power), black (ground), and gray (dial light).

04-17-2014, 10:54 PM	#4
thefraze_1020 Registered User Join Date: Mar 2014 Location: Mount Vernon, WA Posts: 417	Re: Wiring Harness Interchangability 84 Truck, 72 Engine I installed an AM radio in the dash tonight, and all I've got to do is wire up speakers and use butt connectors for the yellow/black/gray wires. __________________ Cameron 1984 Chevy C20 Custom Deluxe



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