One day, my brother drove up in a newly purchased, used, early 80s Chevy 4WD Camper Special long-bed pick-up truck. He was really happy with his purchase. We were checking out the truck when he mentioned a problem that he was having with faulty brake lights. I thought this should be a simple fix.
I was a young college student at the time, familiar with all matters of electronics and vehicle wiring. I had built and wired a tube-frame dune buggy and had done many other automotive and wiring projects. So tracking down this problem should have been a no-brainer.
I started with the fuse. This truck was equipped with an AGC/3AG style fuse block. These are the type with the glass tube and metal caps on either end. A quick visual inspection verified that the fusible element was still intact. Next, with a quick twist-and-pull, the bulb was in my hands. The filaments looked OK, but I verified that both filaments lit with a quick battery test.
So, I scratched my head a little and then decided to check the continuity of the wiring. Not having a diagram or familiarity with how the loom was run, I began at the tail light and worked my way forward, inching my way under the truck as I tested. All the wiring from the brake switch rearward checked out OK. I verified the operation of the switch and then started looking at the wiring forward of the fuse box. I was able to verify power on the hot-side of the fuse block. But surprisingly, there was no power on the input to the switch. My next thought was to check to see if there was a broken wire on the back side of the fuse block. A quick inspection proved that everything there was in place and as it should be.
Then the light went off (no pun intended). I pulled the fuse and did a quick continuity test with my kit-built Micronta VOM meter, only to find that the fuse was defective. It had an open contact that was not visible behind the metal cap. I couldn’t believe this luck. It had never happened before this, and hasn’t happened since.
I dropped in a replacement fuse and everything worked as new. To this day, I’ve never looked at another fuse. If a fuse is involved, I grab a meter and run a quick continuity check. It’s an embarrassing lesson that I learned, and learned well. I freely pass it on to spare others the same fate.
This entry was submitted by Eric Chesak and edited by Rob Spiegel.
Eric Chesak is director of engineering and manufacturing at a small aerospace company in El Paso, Texas. He received a BS in Applied Physics at the University of Texas at El Paso, and an MSME at the University of Texas at Austin. With nearly 20 years of professional mechanical and electrical design experience, he still enjoys the hands-on experience and learning new lessons.
Tell us your experience in solving a knotty engineering problem. Send stories to Rob Spiegel for Sherlock Ohms.