S10 Electrical Problem

I have a 1987 Chevy S10 long bed pickup. Its a 5 speed, no A/C, and no power accessories. The battery is brand new and the alternator is the original. The truck has 80,000 miles. The truck always starts even though I only use it once a week. There is an electrical short and the symptoms are:

When the engine is started, you notice the charging, fuel, and temp guages all go to the bottom. For example, the fuel guage drops to about 1/4 of a tank if you had 1/2 tank of gas. If you turn the headlights on, both turn signal interior guage lights begin to light up. The exterior turn signals work fine. The radio will not work when the headlights are on. I brought the alternator to Pep Boys and had them put a load on the alternator and run it or 10 minutes and they say it checks out fine. I was thinking it could be the battery cables. Any other tips would help.

Thanks, Mark

Do you have a voltmeter? With the engine running and no electric loads you should read about 14 volts at the battery. If you have it there then you need to check downstream. If the starter motor turns over good the cables are most likely good.

I saw something like that many years ago. The insturment gauges were all screwed up and the alternator light was on all the time. Problem was that the fuse supplying the instrument panel blew. Then when the engine was running the power came through the alternator lamp to supply power to all the gauges (Normally that 12 volts would just buck out the

12 volts coming from the fuse). As a result all the gauges were reading low too. I really doubt that it could be a fuse but worth a look.

With the headlights affecting things the way they do I lean towards saying it could a grounding problem. Verify you have a good ground from the engine to the chassis and battery.