Old trucks can hide surprises. Rewiring wasn’t originally on the menu for our Ultimate K10. At our project headquarters, GM Truck Center redid the fuel system (Dec. ’11) then connected the existing wiring to the new fuel pump. The truck cranked but wouldn’t fire. Troubleshooting uncovered multiple issues: wires to nowhere, snipped leads at the electric fans, an intake manifold and EFI harness that were in the early stages of removal, missing and broken gauges, rodent droppings, and more. After half a day of detective work, the unexpected upshot concluded that sorting out the existing wiring would be more time-consuming and less reliable than starting from scratch.
Painless Performance’s rewiring kits have a plug-and-play reputation. For popular vehicles, the company offers application-specific kits. Among their numerous advantages over “universal” kits are wires that follow the original color codes and end in OE-style plugs. The kits’ better-than-stock features include blade-style ATO fuses as opposed to the earlier trucks’ stock glass-housed ones in addition to circuit ID labels printed on the wires’ insulation. The box even contains grommets, zip-ties for securing the wires, a variety of crimp-on connectors and terminals, and a step-by-step instruction manual.
Painless Performance offers 12-circuit and 18-circuit direct-replacement harness kits for ’73-’86 GM trucks with keyed steering columns. We opted for the 18-circuit system (PN 10205) to accommodate any nonfactory electrical additions down the road. (The truck has Flex-a-lite electric fans as one existing example.) The Painless Performance catalog includes numerous other possibilities, including several different fan controllers. The company also has most of the odds and ends necessary for custom installations, such as 1-gauge battery cable kits.
Although rewiring a truck that has minimal power accessories can conceivably be done in a day, Painless Performance advocates patience. Aesthetics and reliability often go together. Remember to loosely route, mount, and bundle the wires. Secure the wires only after finalizing all routing and terminating.
Mismatched pigtails and plugs due to model-year variations and aftermarket accessories can often be sourced at the local parts store. The Painless kit includes extra male and female bulkhead connectors in case replacement plugs need to be swapped onto the harness. If this is necessary, Painless recommends installing the bulkhead connectors with a roll-crimp tool, available from electronics stores such as Radio Shack.
Painless’s IP gauge leads are prewired for plug-and-play ease. GM Truck Center didn’t like our 37-year-old gauges’ condition (some were missing), so it recommended upgrading to aftermarket replacements on a custom panel, which we’ll show in a future article. Low-buck at-home warriors can source OE gauge fix-its from specialists such as LMC Truck.
The Painless instruction sheet includes wiring options for circuit-specific variations among model years. This includes different alternator options, turn signals, headlights, dimmers, and more. Also, the Painless harness includes a circuit for the heater and blower. For air conditioning, the original circuits are retained; the kit’s instructions include a wiring diagram for integration.
PhotosView Photo Gallery
If history is any indication, this truck’s Warn winch will see excessive action, as will its ARB 12-volt fridge. To provide top-shelf reserve capacity and discharge/recharge deep-cycle capability, dual Optima BlueTop marine/RV batteries are a proven solution. They’re made to accept three times as many recharges as standard starting batteries and offer more amps per group size compared to the company’s automotive YellowTop deep-cycle model. Most wheelers already know that Optima’s six-pack sealed construction houses absorbed glass mat (AGM) electrolyte. These batteries are spill-proof and maintenance-free and can be mounted in any position.
To manage the batteries, we’re using Extreme Outback’s new IBS-DBR relay-style dual-battery system. This compact manager links the batteries during charging and isolates them during discharge cycles. The kit’s manual-override button runs the batteries in parallel during discharge for winching and self-jumping. The relay’s housing has a green LED that confirms proper operation. Its red LED flashes trouble codes when a problem happens (say, a missing battery).
For readers expecting body-beautiful modifications this month, we apologize due to unforeseen circumstances. The old wiring harness did its job since 1975, but an extended stint in storage did it in. Rewiring put us behind schedule, but our DC flow is now stronger and more reliable thanks to the Painless harness, dual BlueTop Optimas, and Extreme Outback IBS-DBR battery manager.
The Painless instruction manual is presented so that even first-timers can rewire a vehicle. It assumes that the installer is capable of stripping/crimping and can work a test light and a multimeter. A few basic Painless recommendations:
• Begin by disconnecting all battery cables.
• Before tearing out any wiring, consider identifying it using the labels included in the Painless kit. Documenting the existing wiring with photos or video can assist with replacement-harness routing ideas.
• Save the old wiring in case any pigtails or plugs unique to the vehicle need to be reused.
• Lay out the new harness on the ground to get a general idea of how the various circuits are preassembled. The Painless instructions include a worksheet to help organize the circuits.
• Wire routing can offer several paths to the same destinations. The stock/previous approach is one way; some installers prefer stealthier routing.
• Common sense: Route wires away from sharp, moving, or potentially hot objects. Allow some slack where necessary to compensate for frame and body movement.
• Wires that don’t lie on the floorpan should be supported every 12 inches. (A wire’s dead weight can cause strands to break and/or terminals to come undone.)
• Group wires when possible, using zip-ties and clamps every 6 inches or so.
• Route, reroute, and verify routing prior to cutting, stripping, and crimping.
• Improper crimping is a primary cause of auto-electrical failure. Make sure to use the correct die slot on the crimping tool for the wire-gauge/connector. Also, he-man overcrimping can create connection failure.
• Bad or nonexistent grounds are another common cause of electrical problems. The Painless harness contains black ground wires for the dash and headlight connections. Grounds for other circuits need to be installer-added as necessary.
• Circuits should be tested individually using a maximum 10-amp battery charger: ground clamp to the chassis or engine, positive clamp on the starter’s positive terminal. This tests circuits without overloading them. (Make sure to leave the batteries disconnected.)
• To finish the bundles, Painless recommends zip-tying all exposed wires every 11⁄2 inches or so. Loom material can provide some protection against abrasion, heat, elements, and critters. Convoluted plastic versions are well known. Alternately, Painless offers its new PowerBraid made from flexible PET fiber that’s rated to resist up to 400 degree F.