I have a 1989 GMC s15 4.3 engine auto transmission and I have an electrical problem. The gauges do not work properly and when I turn on the headlight the volt meter drops to about half voltage. The heat gauge will not work properly or does the gas gauge and the dash lights will dim when I turn on the headlights. I have had the alternator checked and it is working fine. The check engine light has come on and also the check brakes light has come on and some times it will just flash on and off. If you hook a computer on to it the computer will say many things are not working properly but this has continued to get worse with time. I have my suspicions but would like some other opinions. Thanks for any help in advance.

I'd begin with checking and cleaning up all connections battery, alternator, starter and grounds. Look for burned wiring (fusible links) and any blown fuses.

There could be a common ground to body that is causing many of the problems. Alternator checked off vehicle may test well - tests on the vehicle are more informative,

T
Tom Greenleaf - MetroWest Boston - USA
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http://www.autoacsystems.com/tomgreenleaf/

Can you or any body else tell me were the common ground is on this pickup. I have replaced the battery cables and checked for fuses. This is what I thought it was but cannot find where the ground is located that control the inside of the cab or dash gauges. Thanks for you help.

Ok: The neg battery cable make one strong ground to the engine block. Either directly from the battery cable or elsewhere the body needs to be grounded as well. There are assorted ones throughout vehicles. I think you'll find one that goes from metal of firewall to back of engine - a bare strap used for ions for this. Others as needed and could be another between body and dash metal to make it a common ground.

You should be able to safely add grounds when needed or just for testing as you may not find a broken orig.

Did the orig (if even the replacement of battery cables were OE) have a separate ground wire on it - the old or the new one? Some come with them some don't. No harm in just using one jumper cable or even strong alligator clip jumper wire to add a good ground - just metal to battery neg and see if things are effected that don't work properly now.

Those straps are old now and contact may be lousy or left disconnected by mistake, broken - who knows now?

Just know that the metal of the body and frame are not automatically grounded by the battery cable to engine block alone. When the loop is unavailable item can try to seek ground thru other items and things go dim, don't work at all, and crazy stuff happens so grounding needs to be a known. You can use a simple test light for detecting a total absence of ground but it would light with the smallest amount,

T
Tom Greenleaf - MetroWest Boston - USA
_________________________________________

http://www.autoacsystems.com/tomgreenleaf/