Diagnosing Voltage Issue May Require a Process of Elimination

Dear Car Talk:

My father is a diesel mechanic but works a swing shift afterward, so he doesn't have much time to help me fix my '97 Honda Civic.

The lights on the Civic will go dim, then flicker, then the radio goes off and then the car just dies. I thought it was the battery, so I had it charged and checked. It checked OK, but the problem continued.

So, my dad comes by at 2 a.m. and puts in a new alternator. He starts it up, and it runs. The next morning, I go to take my kid to school, and it won't start. It cranks but won't start.

I've had friends check the fuses. No issues there. I can hear the fuel pump starting. A friend checked the spark plugs and said they are getting spark but aren't getting the full amount.

I'm at a complete loss. I desperately need my car to be fixed. And I'm running out of ideas on how to fix it. Got any? -- Susan

There are three things I'd ask your dad to look for. Actually, four things, the first being a winning lottery ticket you guys can share. But failing that, I'd look for a bad ignition switch, a loose or corroded wire, or a bad ground.

Have your dad bring over his voltmeter and hook it up to the battery. Then, while the engine is running, try jiggling the ignition switch and each of the wires that comes out of it. Wiggle the wires one at a time, and if you notice the voltage drop while you're wiggling a wire, you've found the problem. If you get no drop in voltage around the ignition switch, try the wires coming from the alternator and battery to the power distribution box under the hood.

This can be a time-consuming process, but since you've already eliminated the battery and the alternator, it's the next logical step.

The other thing that can cause your problem is a bad ground. Since the car is 25 years old, it's possible that its ground wires are corroded or are falling off. There are several of them between the battery and the block and chassis. Have your dad find them and see if they're fully intact. If there's any question, just replace them. That's not hard.

If none of that works, maybe your dad can sneak a nice, no-longer-needed 15-liter Detroit Diesel engine out of his shop next time he's at work and drop that in your Civic. You won't be able to see over it while driving, but you'll have the only Civic in creation that can tow 40 tons. Good luck, Susan.

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