Nov 15, 2011

Trouble Shooting Electrical Problems

It’s an art and a science to diagnose and fix electrical problems when they arise. Obviously, electrical shorts, bad grounds, low voltage transfer, and other problems are not just functionality issues; they are safety concerns. The last problem you want to deal with is an electrical fire in your car because it could burn the car to the ground and take your garage and house with it. To resolve a problem, you need a sound grasp of the principles, the right tools, and the correct working process.

Sometimes during a project, you discover a problem that needs to be resolved before proceeding. As the battery in the Olds rests at 12.6 VDC, I know I have a 1.73-volt drop at the high-beam output of the low/high-beam switch; this is not desirable, and, as a result, the headlights work less than optimally. These kinds of problems are to be expected when you work on a 40-year-old vehicle with extensive wiring modifications. In the Olds, the original builders did not resolve this issue, so it’s time to fix it now.

This Tech Tip is From the Full Book, AUTOMOTIVE WIRING AND ELECTRICAL SYSTEMS, VOLUME 2: PROJECTS.
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After pulling the low/high-beam switch loose, I noticed a few things that were disconcerting. One was that the butt connectors used to connect the switch to the aftermarket wiring got quite warm with the high beams on. Although they pass the standard “pull test,” the heat is an indication of resistance. The second problem was the overall condition of the plug for the low/high-beam switch. The best way to resolve such a problem is with accurate data.

1. Connect DMM across the low/high-beam switch.

That’s right; you want to measure the voltage lost through the switch itself. This is commonly referred to as a voltage drop test. Connect the red probe to the input of the switch and the black probe to the high-beam output of the switch. In the case of this vehicle, these are non-standard colors.

.50 VDC is a bunch of voltage drop across a single switch. Yet, it still leaves almost 1.25 VDC of drop to be found somewhere else.

For now, let’s address the voltage drop across the switch. I removed the plug from the low/high-beam switch, because all of the contacts were in need of replacement.

I removed the plug from the vehicle. After closely examining the contacts, I chose not to reuse this plug. I cut the plug from the mounting base for the low/high-beam switch, because I want to mount the switch back in the vehicle with the plastic base between the switch and floor.

2. Repair the problem.

It’s obvious that my Olds isn’t numbers-matching or even original in the slightest bit. So, I’m okay with totally modifying the connection to the low/high-beam switch itself in an effort to reduce the voltage drop through it. I crimped on 16-14-AWG female push-on connectors—the kind that really bite into the male terminals.

When using female push-on connectors to make solid electrical connections to the mating male terminals, such as those GM used on the low/high-beam switch shown here, always use the type that has curved contact points, such as the two on the right. These get a much better bite on the male terminals than the flat-style ones pictured on the left.

Then, I squeezed them closed very tightly with a pair of pliers so that when I slide them on the terminals to the switch they get a very good bite. Finally, I insulated them with heat-shrink tubing to protect the insulation.

Obviously, the headlight circuit in the Olds needs more work to be optimized.

Written by Tony Candela and published with permission of CarTech Books

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