Vannin' Home Forums General Discussion Electronics For those who like a challenge: mysterious blown fuses.

I have a 1990 Chevy G20. I took a 2600 mile road trip with it last summer with no problems! But after the trip, it started blowing some fuses: the 20a stop-hz fuse and the 20a turn b/u fuse.

I can follow instructions, but have no idea where to start to fix this problem. Here are a few symptoms:

The volt meter on the gauges reads very high, about 17 volts when the van is running. I've replaced both the battery and the alternator. Using a multimeter, the battery reads 12v with engine off, and 14v engine on. Normal.

When i replace the fuses and put on the hazard lights, the stop-hz fuse immediately blows, with the engine off. The turn-b/u fuse is fine for now.

The LR turn signal bulb wouldn't blink, so I pulled the housing to have a look. The bulb is stuck in there like you wouldn't believe.

Before my trip, I put in a new head unit, and put some speakers in the rear where before there were just holes with wires hanging out. I doubt that it's worth mentioning, but who knows?

So, where can I start to solve this problem?

Bad ground somewhere?

Just guessing. Electrical is still a mystery to me.

If the alternator is externally regulated, make sure the voltage regulator body is properly grounded

(1) check all the bulbs to make sure they are the right ones.
(2) if your van has a trailer hitch with trailer wiring, check trailer wiring. Check for any cracked insulation rubbing on the body of bad connections.
(3) check the mounting screws for the rear speakers. Any chance you pierced the tail light wiring harness with a speaker mounting screw?

The volt meter is concerning, but it could somehow be reading a dead short in the system.

Thanks for the quick replies!

The alternator is internally regulated, so no problem there.

Reed: I just made a list today of bulbs that need replacing.
It does have a trailer hitch, and I never thought to check those wires.

I'm pretty sure I didn't puncture a wire while putting in the rear speakers, but I can check.

Someone else mentioned that it could be a dead short. I'll look up what that is, but how can I find where it is?

A dead short is a short between a full (+) voltage source and ground. To find a dead short I would start noting which fuse blows and when. Then you have to get a factory wiring diagram for your car and see what electrical devices are on that circuit and have power going to them at the time the fuse blows.

With your symptoms I would make sure that someone did not install a single filament bulb in a dual filament socket on the left rear taillight, and I would also check out the integrity of the hazard switch. I am not a Chevy guy, so I can't offer more than general suggestions. Your symptoms all seem to be related to the left rear turn signal, but this is just a guess.

Ditto on the voltage regulator if it is external (like ours is) but since you say it isn't... is the alternator grounded?

The Chev/ GM alternators ground via they mounting bolts and adjusting strap, so very doubtfull that is the problem.
You said the brake /hazzard fuse blows when you turn on the hazzards, right? What about when you step on the brake ? If not when you step on the brake, my first thought goes to SOMETHING metalic came loose in the coloum NEAR the hazzard switch and is shorting it to ground,( the main coloum is metal and a ground source) , and this is causing your issues. Could be a tiny screw, spring, DUST can even do it under the riht conditions !
So, I would pull the steering wheel and look around in there for some thing like that near the hazzard switch, best of luck and keep us posted !

Thanks for the tips. I pulled the tail lights to see if I could see anything wrong. The bulbs are stuck in the sockets like you wouldn't believe. Any tips on getting them out? WD-40?

I'll have to get some extra fuses and see what it takes to get the fuses to blow. Like I said, it's the stop-hz fuse blew first, but the turn b/u fuse blows too, I just have usually been driving when it happens.

The alternator is definitely grounded.
I'll have to get a second person so sit in the van and play with the lights so I can watch from outside.

Can I test the bulb sockets with a volt meter to try to find a short?
I'll also check out the trailer hitch wiring when it gets warmer. It just started snowing again.

If the bulbs are rusted tight in the sockets you may need to break the bulb and wrestle the metal base out with a pair of pliers. Be sure to disconnect the battery first. Rusted in bulbs are bad anyway because you need to be able to remove them to replace them. Maybe try sraying a penetrating lubricant such as Knock 'Er Loose or PB Blaster in the sockets and let it soak for a few hours. Are you remembering to push in and then twist counterclockwise? Don't cut your fingers.

One of the bulbs pretty much fell off when I touched it. I mangled it up pretty good trying to get the base out.

I'll wait for a warm day and mess with the bulbs some more, and check the trailer hitch wiring. Thanks for the tips!

When you get the old bulbs out and put the new bulbs in, be sure use some dielectric grease around the base of the bulbs.

Sorry for the delay: I've been out of town and the weather has been bad.

I replaced all of the non-working exterior bulbs, and used dielectric grease as recommended. I can't see much of the trailer hitch wiring, but what I can see looks fine.

I ran out of 20A fuses, so I used 25A fuses and neither blew. I purchased more 20A fuses, and figured out that everything works fine when the engine is not running, but when I try to turn signals or hazard lights with the engine running, the fuses pop pretty quickly.

I replaced the turn signal flasher unit based on a recommendation, but that did not fix anything.

So..... where do we go from here?
My thought is to start testing individual sockets or, but I'm not sure what to check for.

When incandescent bulbs are fed more voltage, they consume more current too, so the engine running having the voltage up in the mid 14's is enough to blow 20 amp fuses but not 25.

But there is still obviously a problem somewhere as these bulbs should not be blowing a 20 amp fuse.

About the trailer wiring harness, the actual connector itself is less likely the issue compared to where the installer took the power from.

They use these wire taps which one places over the wire, and squeezed to puncture the insulation and make contact with the wire.

These will always fail at some point, it is just a matter of time, because the insulation is compromised, and the very act of tapping the wire here breaks a lot of the wire stranding.

So I would investigate the trailer wiring harness where it taps into the original wiring harness. The headlamp switch itself on the dash passes all the current for the signal lights, and the headlamps too. Look for burnt insulation or corrosion at the headlamp switch connector.

get a can of this:
http://www.amazon.com/CAIG-DeOxit-C...28987560&sr=8-1&keywords=CAIG+d5

No other electrical contact cleaner comes close. others just flush dirt and grease, Deoxit removes oxidation, and enhances conductivity of the mating metals.

Do note that Di-electric grease prevents water and oxygen intrusion and thus corrosion, in theory. It also helps heat transfer, it does not clean electrical contacts and does not conduct electricity.
When it gets really old it can actually cause issues.

I believe the wiring harness for the rear lights go over the drivers door and along the upper bulkhead to the rear, where it splits left and right over the left rear cargo door... If any paneling is screwed in that area it may have gone\rubbed through and is shorting when the van moves....

Primary cause is trailer hitch wiring usually though, where some drill the hole through the floor, leave it dangling and do not use a grommet....

Thanks for the replies gents. I'm back at this again. Still haven't solved it!

Something has to be wrong with the left side turn signals, and I highly suspect it has something to do with the left rear wires or plug.

Any recommendations on checking the socket with a volt meter and what to test or look for?