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This illustrations (along with the one below) indicate typical locations where Federal Motor Vehicle Safety Specification (FMVSS) 108 mandates lighting, as identified by required color. Images: Truck-Lite Co. Inc.
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Emergencies occur at the least opportune times. Sink holes appear. Utility lines snap. Storms wash out rights of way. When these things happen, it's absolutely essential that your vehicles and crews be seen, especially if it's at night or in the midst of severe weather.

Along with the other rules that govern public agencies are two guidelines for adequate truck lighting:

  • Federal Motor Vehicle Safety Specification (FMVSS) 108, which requires certain lighting on all commercial vehicles.
  • Federal Motor Carrier Safety Regulations (49CFR393 Part B), which states, “All lamps required by this subpart shall be capable of being operated at all times.”

Lights fail the second criterion from a number of causes: physical and chemical damage, shock and vibration, burnout, and low current.

To keep lamps operating longer, never start a truck with lamps turned on. Surge currents can vaporize filaments on incandescent lights.

And if a lamp appears to be burned out, test it. The top three suppliers recently reported that more than half the lamps returned as defective still worked. Customers not only wasted money replacing those lamps, they missed the underlying causes of the failures—usually the wiring. Then they had to repeat repairs.

Sealed Harnesses = Fewer Failures

A decade ago, lights and wiring were the second-highest truck-maintenance cost category after tires. Since then, most manufacturers have adopted sealed harnesses and LED lighting, eliminating wiring from the list of the top 20 troublemakers.

Still, many fleet managers continue to use sealed bulbs and individual bundled wires leading to each lamp, with ground wires going to the frame. While initially cheaper and easier to repair, over the long run this setup is subject to greater damage than modular sealed wiring.

Coupled with sealed and LED lighting, modular systems reduce overall ownership costs by eliminating exposure to the elements. If you plan to keep a truck more than four years, it pays to upgrade to sealed harnesses. This is especially true if vehicles are exposed to snow-fighting chemicals, which increase the severity of corrosion on truck chasses and components.

A sealed system has a jacket molded right onto the wires and connectors. It's not just a cover; it's a structure. Grote Industries' Ultra-Blue Seal Lifetime Harnesses, Peterson Manufacturing's Maxi-Seal Harness Systems and Truck-Lite Co. Inc.'s Series 88 harness systems virtually eliminate wiring problems.

If you haven't equipped vehicles with sealed harnesses, here are a few tips to help care for discrete wiring:

  • Look for corrosion at terminals. Trailer nose boxes, seven-pin plugs and sockets, and lamp connecters are all vulnerable. For tractor-trailers, Phillips Industries offers J-560 plugs and nose boxes with replaceable parts that make repairs easy and isolate any corrosion that occurs.
  • Check the damage of the wire and any splices for openings that may allow internal corrosion. If wires go through holes in chassis or body parts, make sure the frame grommets are in use and in good condition.
  • Examine the ground wires to the chassis, and replace any corroded or damaged parts. If the chassis is corroded where the ground connects, clean it with a wire brush and emery cloth. Then, reprime, repaint, and reattach with new connectors. It's good practice to paint over the connection with liquid vinyl, sold in parts and hardware stores as electrical-tape in a jar. It will retard further corrosion.
  • If you need to replace connectors, cut wiring back at least ½-inch from the end. Inspect the strands to be sure moisture and corrosive salts haven't migrated between wire strands. Use enough wire to allow a connection with enough slack so that no tension is on the wire.
  • In areas of the country where vehicles are subjected to splash and spray, include a downward-pointing drip-loop to let excess moisture and salts drain away. Avoid arches that allow it to flow into sockets and connectors.
Proper Splicing = Longer-Lasting Repairs

To avoid the need to splice wire, buy replacement lamps with molded plugs or sockets, rather than those with wire pigtails. Protect plugs and sockets from corrosion with dielectric grease. Grote Ultra-Seal Corrosion Protection, Lubriplate DSES, and Truck-Lite NYK Grease are available at most parts stores and truck dealers.

If you must replace wire, splice at a point where the wire is generally dry, and then run the new wire from there. Before joining wires, put an appropriately sized shrink tube over one side. It should be long enough to extend ½-inch past the connectors on each side. When splicing wire to replace corroded sections, include enough wire to form a drip loop. Make sure the loop points downward to allow spray and water to drain away from connectors.

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, which makes 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, or use connecters that bite through 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.

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

Abrasion damages unprotected wires. Protect from abrasion by bundling wires together inside plastic slit-tube conduit available at hardware stores. Use grommets whenever wires are routed through openings in frames, cross members, firewalls, brackets, or panels.

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. Custom-made harnesses are available through authorized dealers.

— Paul Abelson is a former director of the Technology and Maintenance Council of the American Trucking Associations, a board member of Truck Writers of North America, and active in the Society of Automotive Engineers.