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Old 09-19-2019, 07:25 PM   #1
Dleslie212
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Wiring harness recommendations?

I'm going to try to tackle a replacement wiring harness for my 77 K10. Does anybody have any recommendations on a new harness? I was looking at this one:

https://www.painlessperformance.com/wc/20205
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Old 09-19-2019, 07:43 PM   #2
Bandit130
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Re: Wiring harness recommendations?

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Old 09-20-2019, 01:43 PM   #3
hatzie
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Re: Wiring harness recommendations?

Painless and other one size fits all harnesses are not pre-terminated. You'll have to terminate the engine bay wiring and a good chunk of the cab wiring too. More importantly you end up with Frankenstein wiring that has no documentation. I refuse to work on vehicles with "NEW" Painless etc wiring harnesses.

Just because the TV shows replace the harnesses doesn't mean you have to. Painless etc are sponsoring them so they use their products visibly. If yours works and it's not all chewed up spend your money elsewhere.

If your cab harness is bodged to death get a reasonably un-molested cab harness from a 79-82 truck.
You'll get the ATC/ATO plug in fuses, the bulkhead plug will fit and the cab and the engine bay harness plugs in your 1977, and the inside the cab wiring will plug into the switches and cluster in your cab.

It's real intimidating when you look at it as a whole...

There really aren't that many circuits on these trucks and there are several separate sub-harnesses off the bulkhead plug so you usually aren't rebuilding the everything.

If one of the engine bay sub-harnesses are fouled up you can build up a repair harness your darnself.
If it's just one or two wires just replace those wires.

If you have melted or damaged plugs in your engine bay grab them from the yard. If your engine harness is butchered grab one off a donor and start with that as a template. You can extract the terminals from the plastic connector shells and re-use the plastic shells.

Starter has a handful of wires... Crank, Cab Power, J stud power, and Battery.
The engine has three wires... HEI, Temp sensor, and Oil sensor.
Alternator has three wires... Sense, Field, and Charge.
Forward lighting and horn is so simple a caveman could do it. Six hot wires from the bulkhead and grounds on the rad support.
Rear lighting is even easier... four wires... OR six if you add in 10 ga Blue trailer brake and Orange trailer battery wires.
Wipers/washers are five wires...

Heater AC is a completely separate sub harness you can rob from a donor. A single wire plugs in under the dash and runs up to the controls. The rest of the HVAC harness runs out the the engine bay through a rubber strain relief.

Dual gas tanks are a separate harness.

If you're rebuilding a sub harness you use new terminals crimped to new wires in the original connector shells and you're off to the races. Everything plugs in and it can be serviced with the original service manuals.
__________________
1959 M35A2 LDT465-1D SOLD
1967 Dodge W200 B383, NP420/NP201 SOLD
1969 Dodge Polara 500 B383, A833 SOLD
1972 Ford F250 FE390, NP435/NP205 SOLD
1976 Chevy K20, 6.5L, NV4500/NP208 SOLD
1986 M1008 CUCV SOLD
2000 GMC C2500, TD6.5L, NV4500
2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263
2009 Impala SS LS4 V8


RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...Please include at least the year and model in your threads. It'll be easier to answer your questions.
And please let us know if and how your repairs were successful.

Last edited by hatzie; 09-20-2019 at 02:11 PM.
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Old 09-21-2019, 04:22 PM   #4
Bloodhound
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Re: Wiring harness recommendations?

I went with American Autowire. It is a big job and you do need the specific crimpers that they will rent to you or sell. But I am very happy with the quality of it.
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Old 09-22-2019, 09:15 AM   #5
Dleslie212
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Re: Wiring harness recommendations?

Quote:
Originally Posted by hatzie View Post
Painless and other one size fits all harnesses are not pre-terminated. You'll have to terminate the engine bay wiring and a good chunk of the cab wiring too. More importantly you end up with Frankenstein wiring that has no documentation. I refuse to work on vehicles with "NEW" Painless etc wiring harnesses.

Just because the TV shows replace the harnesses doesn't mean you have to. Painless etc are sponsoring them so they use their products visibly. If yours works and it's not all chewed up spend your money elsewhere.

If your cab harness is bodged to death get a reasonably un-molested cab harness from a 79-82 truck.
You'll get the ATC/ATO plug in fuses, the bulkhead plug will fit and the cab and the engine bay harness plugs in your 1977, and the inside the cab wiring will plug into the switches and cluster in your cab.

It's real intimidating when you look at it as a whole...

There really aren't that many circuits on these trucks and there are several separate sub-harnesses off the bulkhead plug so you usually aren't rebuilding the everything.

If one of the engine bay sub-harnesses are fouled up you can build up a repair harness your darnself.
If it's just one or two wires just replace those wires.

If you have melted or damaged plugs in your engine bay grab them from the yard. If your engine harness is butchered grab one off a donor and start with that as a template. You can extract the terminals from the plastic connector shells and re-use the plastic shells.

Starter has a handful of wires... Crank, Cab Power, J stud power, and Battery.
The engine has three wires... HEI, Temp sensor, and Oil sensor.
Alternator has three wires... Sense, Field, and Charge.
Forward lighting and horn is so simple a caveman could do it. Six hot wires from the bulkhead and grounds on the rad support.
Rear lighting is even easier... four wires... OR six if you add in 10 ga Blue trailer brake and Orange trailer battery wires.
Wipers/washers are five wires...

Heater AC is a completely separate sub harness you can rob from a donor. A single wire plugs in under the dash and runs up to the controls. The rest of the HVAC harness runs out the the engine bay through a rubber strain relief.

Dual gas tanks are a separate harness.

If you're rebuilding a sub harness you use new terminals crimped to new wires in the original connector shells and you're off to the races. Everything plugs in and it can be serviced with the original service manuals.

Thanks for the recommendation. The wiring in mine is so messed up because of the PO. The reason was thinking Painless was because they're documented really well, with each wire marked every few inches exactly what it's for. I'll be the first to admit I am terrible with electrical - I don't know anything about it.
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Old 09-22-2019, 09:31 AM   #6
hatzie
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Re: Wiring harness recommendations?

Quote:
Originally Posted by Dleslie212 View Post
Thanks for the recommendation. The wiring in mine is so messed up because of the PO. The reason was thinking Painless was because they're documented really well, with each wire marked every few inches exactly what it's for. I'll be the first to admit I am terrible with electrical - I don't know anything about it.
Download the wiring manual. You can likely print the 11.5x36 pages at FedEx office if you can't find the printed manual on evilbay.

It's fairly straightforward. 1978-82 are darn simple harnesses... as I pointed out.

You'll find it's not as intimidating as you think.

Ask questions. If you don't know it's not a stupid question .
__________________
1959 M35A2 LDT465-1D SOLD
1967 Dodge W200 B383, NP420/NP201 SOLD
1969 Dodge Polara 500 B383, A833 SOLD
1972 Ford F250 FE390, NP435/NP205 SOLD
1976 Chevy K20, 6.5L, NV4500/NP208 SOLD
1986 M1008 CUCV SOLD
2000 GMC C2500, TD6.5L, NV4500
2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263
2009 Impala SS LS4 V8


RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...Please include at least the year and model in your threads. It'll be easier to answer your questions.
And please let us know if and how your repairs were successful.

Last edited by hatzie; 09-22-2019 at 12:11 PM.
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Old 09-22-2019, 12:04 PM   #7
dmack91
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Re: Wiring harness recommendations?

A friend bought an AA harness for his nova. I wasn't impressed. None of the connectors were installed, just included in bags. The wire bundles were no different than the 20 circuit universal kit I put in my 1950 Ford F1.

My k20 wiring was beyond hacked up by a PO. I went to a wrecking yard and pulled a good one from a donor truck. Fairly simple swap.
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Old 09-22-2019, 07:59 PM   #8
Bloodhound
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Re: Wiring harness recommendations?

Quote:
Originally Posted by dmack91 View Post
A friend bought an AA harness for his nova. I wasn't impressed. None of the connectors were installed, just included in bags. The wire bundles were no different than the 20 circuit universal kit I put in my 1950 Ford F1.

My k20 wiring was beyond hacked up by a PO. I went to a wrecking yard and pulled a good one from a donor truck. Fairly simple swap.
Mine has many terminated ends with connectors installed. In fact most were. They don't terminate them all because it wouldn't make sense to, a lot are vehicle specific.
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