Q: The alternator on my Chevy pickup isn’t keeping the battery charged consistently. My mechanic has replaced the voltage regulator twice, and now he wants to replace the alternator for a second time. He charges me $50 every time I come in to get it checked, before he even really does anything.

What’s going on? And is there any way for me to test these things myself?

A: I’m going to assume that you’ve troubleshot all the wiring in the charging system, including the ground cable to the engine block, the frame and the battery’s negative terminal. Poor connections make even a brand-new alternator/voltage- regulator combo perform in- adequately.

Check for voltage drops along both positive and negative legs of the circuit. You’ll need a simple $15 multimeter for this.

Ready? Your GM vehicle uses a Delco alternator. On most Delco alternators, you can simply insert a screwdriver into a D-shaped hole in the back of the case and ground out the voltage regulator. This is called full-fielding the alternator. It bypasses the voltage regulator and forces the alternator to put out 100 percent of its capacity.

Take your voltmeter — or use the one on your instrument panel, if you have one — and monitor the alternator output while you do this. In a minute or two, you should see the voltage rise steadily from 12.6 volts with the engine off to 15 to 16 volts with the engine idling. Pull out the screwdriver, and the voltage should drop to 13.5 to 14.5 volts, depending on the state of battery charge and temperature. Don’t let it get above 16 volts or so, but pull out the screwdriver before you fry something.

It may, in fact, not be your alternator. Test it: If the voltage doesn’t climb steadily, it’s a bad alternator. If the voltage does climb, but returns to less than 13 volts, it’s probably a bad regulator.

Q: I have a Jeep Wagoneer. The mechanic was trying to test the electric fuel pump, applying 12 volts directly from a battery to the terminals of the pump, lying on the ground outside the fuel tank. Another mechanic was cranking the engine, while a third was checking the fuel pressure with a gauge connected to the fuel-pressure regulator.

Apparently enough gasoline passed directly through to the cylinders that the space between the cylinders and pistons was filled with gas, and the engine wouldn’t crank. The level of oil on the dipstick went up an extra 4 quarts, so we changed the oil and filter.

Could this have caused any internal damage to the engine?

A: I’m not exactly sure how they did it, but they managed to hydrostatically lock the engine by filling at least one combustion chamber with more liquid gasoline than the residual volume in the cylinder at top dead center. Somehow they must have kept the fuel injection spraying fuel into the intake ports for quite awhile. Maybe there’s a leaky injector that dribbled fuel into the engine.

Jumpering the fuel pump to test its pressure output, in and of itself, won’t do any damage. And filling the combustion chamber with fuel shouldn’t have caused a major problem either. The extra 4 quarts of oil you drained out of the crankcase came from the cylinder or cylinders that had filled with gas, because the gas trickled past the rings into the bottom of the engine, diluting your oil. Again, no long-term problem.

One remote possibility: If you tried to start the engine, and one cylinder fired and spun the crankshaft merrily along until the partially filled cylinder brought everything to a catastrophic halt, there might be a bent connecting rod, a cracked piston or a bent crankshaft. Don’t ask how I know this, but any of these will make a really big, ugly, banging noise when it happens. Since you didn’t mention this sort of noise, chances are it didn’t happen.

The starter motor alone won’t spin the engine over fast enough to damage anything.

Q: I have a new SUV. Both brake lights and the high-mounted center brake light come on when I step on the brakes, but the light on the driver’s side is very dim. I would say that it is about half as bright as the right-side one.

I have tried cleaning the socket connections, swapping bulbs and even replacing the old bulb with a new one. All the other lights work as they should.

Any suggestions?

A: I’d bet lunch that the ground connection to the socket on the dim side is poor. Find the ground-connection point and loosen it up. Clean out any corrosion, and tighten up the nut and lockwasher to establish a positive connection.