Would you trust an original electrical cord on a well-used kitchen appliance that’s pushing 40 years old? Well, how about if its insulation was brittle and cracking, and the copper wire strands were showing? An electrical short could blow a household fuse or circuit breaker, damage the appliance’s internals, or in the worst possible case, even create a fire. Assuming the appliance is in excellent working order otherwise, simply replacing its cord is the smartest solution.

Apply this to the wiring harnesses in your vintage Pontiac. Many of our beloved possessions are nearing or have pushed past the 40-year-old mark. In that time, while such vehicles were used as daily transportation and the wiring harnesses throughout them were subjected to any combination of temperature extremes, moisture, general wear, and age. The result today is often rusty, corroded, and/or loose connections or bulb sockets, which can lead to erratic operation.

Our particular ’76 Firebird is not an exception. While its interior wiring was sheltered from the elements and is otherwise in seemingly excellent condition, the harnesses found under the hood and in the trunk compartment had seen better days. A quick call to M&H Electric Fabricators in Santa Fe Springs, California, and a few hours was all that was required to replace our Pontiac’s aged original harnesses.

Here’s how we did it. The last time we worked on our Trans Am’s 455, we noticed that some of its engine-harness wires were brittle and frayed. The oil-pressure and temperature sending-unit leads were loose and the retaining clip on the wire that powers the HEI had broken off long ago. Its original taillight harness had one dead socket and a couple others that appeared suspect, too.

It’s not uncommon to find that a previous owner or mechanic unraveled one or more of your Pontiac’s wiring harnesses in the past to repair a damaged wire or socket. While we could have certainly performed similar surgery to correct the issues found within ours, the splicing creates another joint, which invites resistance or failure, and it doesn’t look factory stock. We decided it was best to explore our replacement options.

Complete wiring harnesses that fit and function exactly like originals is what M&H is best known for

M&H Electric Fabricators has been reproducing wiring components for vintage vehicles of most any make for nearly 30 years. In addition to its line of cables and switches, its breakerless conversion kit for points-type distributors is among the easiest to install presently on the market. Complete wiring harnesses that fit and function exactly like originals is what M&H is best known for, however, and its in-depth catalog includes most any vintage Pontiac on the road today.

“All of our harnesses are hand assembled in the U.S.,” says Mike Randal, general manager at M&H. “Ours feature original factory-type connectors, terminals, fuseboxes, and conduits to ensure easy installation. The wires match the factory-original color codes and gauge sizes, but ours are constructed using wire that’s much more tolerant to heat than the originals. Our U.S.-made wire is temperature rated to 257 degrees F, where the originals are rated to only 176 degrees. The harness is then wrapped with the correct non-adhesive or cloth-woven tapes to assure a factory appearance.”

When it came time to consider new wiring for our Firebird, we were confident that M&H had us covered. A quick trip through its detailed Firebird-specific catalog revealed that it reproduced literally every possible harness any ’76 Trans Am could’ve been assembled with. We set out to determine the condition of all existing wiring harnesses in our particular car to determine those needing replacement from those that could remain. We inspected for weak or brittle insulation, frayed connections, and/or loose or corroded bulb sockets.

Ultimately we elected to replace these harnesses: forward lamp ($205), engine ($181), tachometer ($32), and rear lamp ($200). While M&H filled our order directly, it noted its products are also readily available through such HPP advertisers as Ames Performance and Year One, so be sure to check with your preferred retailer. Within a few days the harnesses were on our doorstep, and we noted their factory-stock appearance and plug-and-play install. The swap was easy, done quickly and according to plan.