I must have a short circuit

I pulled all the fueses and used a test light in place of the fuse, over half of the circuits gave light, indicating a short, the other circuits gave no light, switch on or off, I am puzzled, could it be in the computer brian? where do I go from here, Thanks, Jim

over half of the circuits gave light, indicating a short

Well I would say that over half the circuits indicated some power usage. Modern cars are full of computers and stuff that use energy even when off. You may want to do the same thing, but this time measure the current (not voltage).

You’re not testing correctly, so your results are invalid.
What problem are you actually having? Battery draining?

Yes the battery drains, but yesterday I had the battery charged and when I opened the door the interior lights were very dim, then I turned on the head lights and no lights, so I tested the battery again and it read 14 volts, so I removed the cables and cleaned them and put them back on the battery but no change. My heater switch only runs on high speed, and motor used to growl alittle in lower speeds but now nothing, and why would the cicuit for the 4WD 25A and the radio 10A be dim? This is a GMC 1995 1/2 ton with only 113,718 miles. Thanks

Most frequent place I have found a draw in your type truck is with the light in the mirror in the sunvisor.
I hope you don’t decide to make food money off your electrical diagnosis skills but I have seen worse, what were you thinking?

I spent 12 weeks in a daily basic electricity class offered by ITT. At the graduation for that quarter the instructor (ex U.S. Air Force electronics instructor) told us we now know more about electronics/electricity than 99% of the population, I am now convinced he was right.

Now clean or replace the other ends of those cables. Also bend the cables to feel any rustling or crunching inside. This won’t solve your battery drain problem but might fix the dim lights.

I assume you have a battery drain issue, check to make sure the door plunger switches are working properly.

I suggest you purchase a meter that is capable of reading up to 10 amps of current if you are trying to solve the trouble yourself. The trouble you are having may be in the circuit for the 4WD. I suspect the radio drain is ok since it needs current for the memory. Here is a link that discusses how to test things.


The blower problem you are having is most likely due to bad resistors for the speed control. Follow the wires back from the blower to find the resistor block mounted on the ducting.

I want to thank all of you for your help, I now understand my digital multimeter better, and have used it to test the circuits again and have found two that read .90 and 1.30 in the unfused range, by the way, my visor mirror does not have a light, so that is not the problem. Thank you all again, jotheuser