The Amateur Amateur: Mobile Flambée

By Gary Hoffman, KB0H
Contributing Editor
October 15, 2001

This time, we highlight the hazard potential of mobile installation power wiring. A proper mobile installation should include adequate fusing. Before installing mobile power wiring, you should first make sure the wire will handle the required current. A check in the Component Data chapter of The ARRL Handbook for Radio Amateurs should provide a good guide. Adequate and well-placed fuses are necessary to prevent fire hazards. For maximum safety, fuse both the hot (positive) and ground (negative) wires near the battery. Automobile fires can be both dangerous and costly!

My wife Nancy and I have been married for 30 years. I love her very much. I know she must love me as well because she didn't yell at me when I set our car on fire.

We decided to take a trip to England to celebrate our 30th anniversary. We were leaving on the evening of Labor Day. Prior to leaving, we needed to take our Labrador retriever, Thor, to the kennel. We all piled into my car. Almost as soon as I had turned on the ignition Nancy said, "What's that terrible smell?" Suddenly dense smoke poured from under the hood.

Nancy, the dog, and I bailed out of the car, our eyes streaming and our throats raw from the acrid smoke. "I'll take Thor to the kennel," Nancy managed to gasp. The implication was that I would stay home, figure out what had happened, and prevent the house from catching fire. Nancy and the dog made a fast transfer to her car and burned rubber out of the garage before they asphyxiated.

I hustled down to the basement to get some fans. I grabbed two and was struggling up the stairs when a very loud siren began to wail. Cold fear gripped my heart. Oh no, the garage is on fire! I thought. Fortunately that wasn't the case. It was the first Monday of the month and St. Louis County was just performing its monthly test of the tornado warning sirens.

I set up the fans to blow the smoke out of the garage. I opened the hood of my car and saw that there were no flames, so whatever had happened was probably over. The smoke was still too dense for me to stay in the garage so I retreated into the house and let the fans do their work.

When I was able to re-enter the garage, I peered into the engine compartment of my car. Everything seemed in order at first, but I finally spotted the culprit. Some of the electrical wires I'd recently installed to power my ham radio were fried to a crisp. One set of wires seemed intact but the second set had been completely destroyed, the insulation having literally burned off of them.

I knew immediately what had happened. When I'd had a mechanic install the wires, I'd asked him to run a set to the trunk to power my ham radio. I'd also had him run a second set into the passenger compartment, since I eventually planned to install a different radio in there. The wires in the passenger compartment had been coiled up and put under the floor mat of the driver's foot well. I had completely forgotten about them.

One end of the unused set of wires was connected to the battery. The other end, lying under the driver's mat, had simply been snipped with a pair of cutters. They weren't connected to anything. Foolishly, I hadn't thought to cap or insulate them. Nothing had happened until that day, when we were about to depart for England. Then fate decided that it was finally time for the bare end of the positive wire to touch the bare end of the negative wire. They formed a short circuit and electricity flowed freely. The wires got hotter and hotter and quickly melted their insulation, causing the acrid smoke.

My car with its doors and hood open--starting over again.

But luck was with me. The car was undamaged, there was no fire and Nancy did not strangle me with the dog's leash.

I used a pair of cutters to disconnect the burned wires from the car's battery. With great regret, I also cut the wires leading to the trunk and powering my ham radio. They had been partially melted where they had come into contact with the other set of wires, and by this time I was extremely safety conscious. Thus satisfied that the car wasn't likely to burn up, we went on our vacation.

Upon our return from England, I bought some new wire. I was very gun shy at this point, but I just couldn't live without my mobile transceiver. I also couldn't face the prospect of my hygienically challenged mechanic looking under the hood, then turning his gaze to me and slowly shaking his head, unable to believe that any creature on Earth had done something so stupid. So, I decided to install the new wires myself.

With my car's rocker panel exposed, I was able to follow the route of the old wiring.

It wasn't so terrible. I'd originally had the mechanic run the wires because I didn't know where to put them, how to get through the firewall, and things like that. This time I just followed the existing wires (or in some cases, the trail of scorch marks). The wires leading to the trunk were largely undamaged, but I replaced them anyway. The wires to the passenger compartment were fried to a crisp in some places and melted into a puddle of slag in other places. I scraped up the ashes and peeled up the melted plastic and ran new wiring.

I did everything the mechanic had done, with one notable exception. He had tied the two sets of wires together and clamped them into the same lugs at the battery. I installed completely separate lugs on the two sets of wires and did not connect the spare set to the battery. In fact, I wrapped the spare wire lugs in so much electrical tape that it will take a chain saw to free them. I also heavily insulated the ends terminating inside the car, something I should have done the first time. (Editor's note: Fuses also should have been installed near the battery end of both sets of wires as well.)

Some melted remnants of the old wiring.

Being hypersensitive about safety this time, I double, triple, and quadruple-checked everything. Every time that I touched a wire I put a meter on it to make sure that it was the right one. I cleaned up everything and spent a nervous ten minutes looking for a missing tool (it had slipped into the crevice of the back seat). When I was absolutely sure that I had done everything properly, I pressed the power button on the mobile radio. Nothing happened.

I decided to check the trunk first. Fortunately, the problem was simple and obvious. I'd forgotten to plug in the radio. I quickly remedied the situation, jumped back into the car, and tried the power button again. The radio came to life! It hadn't been damaged. It hadn't lost its programming. It worked just fine. I was ready for my next radio adventure--as long as it didn't involve smoke.

Editor's note: ARRL member Gary Hoffman, KB0H, lives in Florissant, Missouri. He's been a ham since 1995. Hoffman says his column's name-- "The Amateur Amateur"--suggests the explorations of a rank amateur, not those of an experienced or knowledgeable ham. His wife, Nancy, is N0NJ. Hoffman has a ham-related Web page. Readers may contact the author via e-mail,[email protected]

© 2001 American Radio Relay League