My car has several electrical problems

Question:

I’m the second owner of a 34,000-mile 1980 El Camino. My stepfather was the original owner. It runs great and the 305 cid engine and automatic combination has lots of pep. However, the car has some electrical problems.

When I get in and buckle up and start the engine, the warning buzzer starts howling and continues doing so until I get down the road for a minute or so. Then it kind of fades out. Also, the tach and gas gauge don’t work right. Before the car is started, the gas gauge is pegged to full. After I start the car, it stays pegged. The tach is pegged all the way before the car is started then after it’s started the tach needle falls back and then pegs all the way to the right again. The oil pressure, water temperature, and charge gauges all work fine.

Sometimes after a long drive, the gas gauge falls back and starts registering the gas correctly but once I turn the engine off and start it up again the gauge is once more pegged.

I thought the problem with the gas gauge was most likely the sending unit or a bad ground back by the tank so I pulled the tank and replaced the sending unit with a junkyard unit.

I also cleaned the ground connection but there was no change in the problem. Now I’m puzzled!

Answer:

The problem with the seat belt buzzer continuing to sound even after you buckle up and are on your way is probably due to a malfunction in the switch or the relay.

I believe it’s more likely to be in the relay so this is where I’d look first.

The instrument problems you’re experiencing are due to one or more faults in either the instrument, its wiring circuit or the sending unit. While you can’t be entirely certain, in all likelihood the fuel gauge sending unit is probably not the problem since the replacement unit you installed didn’t fix it.

To eliminate the sending unit for sure, remove the sending unit wires at the tank and attach them to a resistance bridge. This is a gauge-testing tool that enables you to change the resistance.

When the resistance changes, the fuel gauge should sweep smoothly between empty and full. If the gauge works correctly with a resistance bridge then there is something wrong with the sending unit or the connection to it. If the gauge doesn’t work then either there’s a problem in the wiring or with the gauge itself.

If you connect the resistance bridge directly to the gauge, bypassing the wire harness that extends from the sending unit to the instrument cluster, you can determine whether the problem is in that harness or in the gauge. If you determine that the problem is in the wiring, it is most likely at one of the connection points.

Your tachometer problems can be due to a defective tach, something wrong with the wiring, a bad tach filter, or a malfunction in the trigger signal source. The erratic behavior of your tach suggests that the problem may more likely be in the tach’s circuit board.

Carefully look at the circuit board on the reverse side of the tach and test the solder traces for interruptions.