The best way to fight corrosion is to keep road salts away from copper wiring. These wires are not protected.
Brad Van Riper, Truck-Lite Co. The best way to fight corrosion is to keep road salts away from copper wiring. These wires are not protected.

A reader wrote to tell me that the safety lighting on his dump truck bodies was flickering. When he checked, the wires and terminals were corroded, and a green powder covered some connectors. So he rewired all the light circuits using new connectors. Two years later, his problem was back.

“Friends of mine with older trucks have gone more than 10 years without problems,” he wrote. “Why? What can I do to stop the corrosion?”


First, the friends without problems may go another 10 years without incident — if the trucks have modular sealed wiring harnesses. They cost more up front, but save money in the long run by reducing maintenance costs.

Sealed harnesses encase wires in insulating covers, with connections between modules that keep corrosion-inducing moisture from pins. With only solid pins exposed and dielectric grease protecting them, sealed harnesses keep water and chemicals from the wire.


Replacement wire ranges from $3 to $15/spool. People tend to buy the cheapest because they've never learned why prices differ: gauge size, amount of copper, and the type and diameter of the insulation.

The most common wire, Type GPT automotive primary, uses PVC insulation rated to about 175° F. Higher-priced SXL or XLP wire, used by most truck and body manufacturers, is stable to more than 250° F.

You want the tightest possible connection without damaging insulation. Fourteen-gauge SXL wire, for example, has a 20% greater overall diameter than 14-gauge GPT. Connectors are made to accommodate the largest diameter in their range, and smaller wire may leave gaps that create a path for salt spray to enter the wire through the connector.


With discrete wiring (individual wires that run from a terminal or switch to the point of use or to a chassis ground), sealing connections is critical. Corrosive spray can enter exposed wire ends and, over time, wick through the strands for 20 feet or more. This is especially true with dump trucks that double as snow-plows and salt spreaders.

Use OEM-grade wiring to seal the connections from moisture. If you want extra protection, you can buy marine-grade tinned copper wire — but if you seal your connections properly, you won't need to spend the extra money.

Use two-stage ratcheting crimping tools to get the best crimp: One die set is for the wire, the other is for the insulation. Do not over-crimp, as you can cut through the individual conductors and reduce current-carrying capacity.

Use crimp connectors with adhesive sealant in the insulation. When you heat the connector, melted sealant will flow around the wires. If possible, solder exposed wire strands after crimping but before using the heat gun on the connectors so you don't remelt and lose the sealant. If you don't remove enough wiring to get rid of the salts that caused the problem, you'll be repairing again in a few months.

Use heat-shrink tubing over the entire wire splice and use the heat gun to mold the tubing around the connector and wire. The best is meltable-wall heat-shrink tubing. When the tubing is heated, a hot melt material fills the repair, adding an additional layer of protection. When plugging terminals into sockets, use dielectric grease to keep out moisture.

Put drip loops in the wiring so spray runs away from sockets and terminals, not into them.