The U.S. Department of Transportation mandates red and amber lights and headlights in these respective areas on ready-mix trucks.

If you must replace a wire, splice it at a point where the wire is generally dry, and then run the new wire from there. Before joining wires, put an appropriate sized shrink-tube over one side. It should be long enough to extend a half-inch past the connectors on each side.

The best splices are made with the wire sections twisted together and soldered. Crimp connectors are almost as strong. The best have sealant that flows when heat is applied, making the connection moisture-proof.

After crimping, test the connectors by pulling gently on the wires and terminals. Even when using terminals with heat-activated sealers, use heat-shrink tubing. When done, use heat on the connector as appropriate, then slide the tubing over the splice. Use a heat gun to evenly shrink the tube to seal the splice.

Never penetrate insulation. Continuity testers with pointed probes are designed for use with metal sockets and plugs. When pushed through insulation, they leave a pinhole that conducts chemicals through capillary action, causing corrosion. Never use connectors that bite through insulation.

Freezing moisture

Bundle and support wire using plastic ties as closely as possible. Moisture can freeze on the wire, and ice build-up adds weight that could pull plugs out of sockets. Also, wire ties reduce vibration.

Abrasion damages unprotected wires. Whenever possible, bundle wires together inside plastic slit-tube conduit available at hardware stores. The tubing helps protect wires from abrasion.

Harnesses that are custom-made specifically for your vehicle are available through authorized dealers. If you must add lights or make repairs, never splice into a sealed harness system. There are “daisy chain” or “plug and play” modular systems available to allow connections for extra lamps without destroying system integrity.

To learn more about lighting, wiring, harnesses, and electricity, Lighting User's Guide and Harness User's Guide are two easy-to-understand booklets from Truck-Lite. They're free at

— Paul Abelson if a former director of the Technology and Maintenance Council of the American Trucking Association. You can e-mail him at truck

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