Finding a short circuit with a multimeter?

[y5mgisi]

Geesh I just seem to have all kinds of problems lately! So, on my 78 gmc the lamps fuse keeps blowing. It used to just blow every few months but now its dead as soon as I turn on the lights. So I thought maybe I could track sown the short circuit by putting a multi meter in ohms mode between the terminal on the fuse block and ground and start disconnecting each light bulb until the reading changed on the multi meter. What do you think? Any advice on how to keep this plan from being retarded?

 

[Fordum]

That will often work. But one little trick. Put it on DC Volts first. If you get a volt reading, find out where the voltage is coming from before you set it to ohms and blow out the meter.
I figured that out after I blew a meter. No matter how sure you are that you have killed the power, its a quick check, and sooner or later will save your meter.

Problem is, its probably not a bulb, and taking out bulbs probably will not show a change.
If you have a schematic, see if there are places you can break the circuit to isolate parts of it.
Then, when the short goes away, you will know what part the short is in.

Good luck, I had an intermittent short in a turn signal that took me 5 years to find.
Mine was not as nice as yours to stay shorted.
Mine would go weeks before it did it, and then would not do it again for weeks.

I mounted a circuit breaker on the dash that I could just reset when it popped. Turned out it was a pinched wire under the edge of the hood that only was a short when I hit a bump.
So, I had to hit a bump just as the right turn signal was in mid-flash for it to short.

 

[Blue71Chevy]

Electrical problems are a pain. fuse blows with just the parking lights on or when the headlights come on? this can eliminate parts of what you need to check. i don't remember if it affected as far back as 78 but there was a few models that if the hazard switch was bad it could cause the short to ground. usually the circuit goes form battery to fuse to light switch to hazard switch to the lights if the hazard was bad as soon as you kicked on the parking lights your 20a fuse is smoke.

now as far ans further diagnosis not sure if i can put to words what im thinking. i dont have a wiring diagram for a 78 i can only go back to 82 but looking at an 82. the front and rear parking lights are wired in parallel, think Christmas lights your front and rear lights are wired like the type of lights where you can remove one bulb and the remaining bulbs stay on if your short is before the splice you will remove all he bulbs and have no change in the meter, if your lucky it could be after a splice and you can narrow it down using your idea. if this process of elimination dosent work ask yourself these 3 questions, where is the wiring most likely to have shorted out? which of these areas can i quickly visually inspect? is there anything else that may not seem related but is not working after the fuse blows? I start with a flashlight and i check common points were wiring can rub though, where it passes though any metal, firewall, front core supports, inner fenders ect, pull on the wiring, gently and inspect the wire where is passes though you should have 1-2 in of play to tug on wires. hopefully you will see something apparent. If you have something that is seemingly not related but stops working when the fuse blows i try to eliminate that item unplug it trace the wires ect see if that's the cause. if not then its time to find a wiring diagram.