77 C30 Dualie wiring harness suggestions?

[mr48chev]

One of my trucks is a 77 Chev C30 dualie with 454 4 speed and not much else. To be PC the wiring harness has seen too many years of roofing worker and landscape worker patches and fixes and is in dire need of a full replacement under the dash and under the hood.

This is my hauls everything tows anything and does the dirty work truck and it seems I work on the wiring undoing messes every time I use it.

What are the best options?

[hatzie]

You may be able to find a decent 1979 -1982 cab and engine bay harness on a donor that's not chopped up.
You'll get the ATC/ATO plastic blade fuse panel with that deal.

New is generally as large a pain as just repairing what you have... I've found that Painless etc universal harnesses are not very painless... The good side is that you get an ATC/ATO fuse panel. The bad side is it comes with a bunch of un-terminated wires with maybe the plug for some random common GM ignition switch... that doesn't plug into yours. You end up with almost as much work as fixing your bodged original if not more.

1977 is pretty simple... not that many circuits. The downside is it has Glass Cartridge fuse panel. Generally the connector shells aren't too bad to re-use and most connectors have easily available terminals inside. All of the terminals you need are available from Mouser, Del City, etc. If you have the tooling you could just replace the wires that were damaged by Gomer and his buddies.

Download the 1977 wiring manual and print off the wide pages at Fedex Office so you can write on them in red pencil without molesting an original copy... They're 11.5"x36" Banner sheets.

Any wire you install should be SXL (Heavy Crosslink Poly) jacketed. The General Purpose PolyVinylChloride jacketed wire will crack and fall apart in a very short period of time.
You can get split poly loom in 250' spools from NAPA and several outfits online sell 50' and 100' sections. You'll want at least 3/8" for the tail and forward lamp harnesses. You may want expanding mesh to protect other wiring.

Generally the big stuff like the ignition switch wiring is un-molested.
Inside the cab it's the heater, lighting, wiper, and radio wiring that gets mickey mouse repairs with butt splices etc.

It's as much a mental excercise as a physical one. Break it up into sub harness sections. As much as you'd like to jump through and fix everything DON'T. Concentrate on the harness section that you chose and fix only that one. If you feel like picking another after your first victim then do that but be sure to finish it. Being "done" is a big motivator... at least for me.

The tail harness is bloody easy to repair. It's usually where I start on a badly damaged vehicle harness... It's almost always bodged quite badly but It's literally just four wires from the firewall plug to the tail end of the frame. Remove the firewall plug and pull the old wires off the frame or just cut em back to the frame on both ends and leave the old mouldy dead wires right there to tie the new ones off on.
Be careful to not cut off the fuel gauge wire... If it's included in the original tail lighting bundle. I usually check the fuel gauge sender wire over when I do the tail lamp harness but leave it alone if it looks OK. If it's chewed up you can get a long Chevy NOVA sender wire with the molded rubber sender pin plug from Classic Industries and mod the firewall end to mate with the truck.
You can make a new front to back tail light feed harness section in about 10 minutes.
First... I usually add two extra long 10ga trailer plug wires to run down the LH frame rail along with the actual tail lamp harness. They should reach past the front and back bumpers. BLUE for trailer brake that has to reach the controller in the cab and RED for breakaway battery that has to reach the J-Studs on the firewall.
I generally replace the chewed up molded rubber plug with an 80's 2x2 4position Weatherpak. Use the 1985 & later pinout for the plug and tee in for the trailer plug with a 1985-1987 CK Hopkins trailer lamp tee.
You use Packard 56 terminals for the firewall plug. Remove the old terminals and insert the new ones on your new harness. Then just plug it in.
If the actual short tail lamp wiring pigtail with the lamp sockets is chewed up you can get a decent replacement from Mr Taillight or you can liberate a decent one that already has the Weatherpak plug on it from any 1985-1991 Squarebody.

I usually move on to the gauge sender/Coil-power harness next. The coil wire is 12ga red SXL. I usually change the BAT connector shell on the distributor to the dual BAT/TACH connector. It fits better than the single terminal connector. This is one on Amazon with Prime shipping...https://www.amazon.com/Pigtail-Harne.../dp/B071ZF99V2
If the three wire pigtail from the HEI cap into the distributor body is damaged get a new AC Delco D221 pigtail. They call em all kinds of things but that's the part number you want. It's bloody easy to change but be sure to clean off and re-coat the ignition module and distributor with zinc heatsink paste before you re-install it.
There are literally only two other wires for the engine itself... Oil pressure and Temp sender. These have Packard 56 terminals on both ends of the wires. Usually they're 16ga Green Temp and TAN Oil pressure... The stock 1977 temp sensor is a Nailhead terminal sensor so it requires an odd Female Packard 56 shell. I just posted info on this in another thread.

NEXT... the starter/alternator wiring... This will require that you build some fusible links and some 10ga wire for the J-Stud to alternator and starter BAT terminals... so get a small spool of SXL 10ga red. On the alternator plug I usually look over the white exciter wire and don't monkey with it if it looks OK and the jacket isn't brittle. If you have gauges the exciter wire has a resistance of 47Ω to the firewall plug so you'll have to put a 1/2W 47Ω resistor inline with a replacement wire. I almost always replace the small gauge red sense wire on that plug because it's pretty chewed up at the starter or firewall studs.

The heater wiring is another quick sub harness but it's a PITA to pull out of the vehicle. I usually lay this one on a sheet of plywood and put finish nails just past where every bend or termination will be and then lay the new wires on the plywood with bread ties to the nails. Small wire ties will hold the wiring in place to slip split poly or harness tape over it... Harness tape is not Electrical tape it's special. It has no glue and requires some experience to use. Split poly or expanding mesh is easier for amateurs like us.

[RogerKoop]

I have access to new reproduction wiring harnesses which are made using GM wiring diagrams. They are exactly like the originals.

Engine Harness with HD Chassis sells for $239.95
Engine Harness with out HD Chassis sells for $219.95
Dash Harness sells for $540.95
Front Light Harness sells for $209.95