Fog lights blowing fuses

[Yoda3000]

Recently my fog lights have been blowing all the fuses i put in. They are both 55W H3 bulbs because I checked them. This should not be happening.

[benebob]

Mine have been doing the same thing since the 10th anniversary meet. I've yet to locate the problem and have pretty much given up on it since I don't drive it in the rain anymore. Let me know if you figure out the issue on yours and I'll have to try the same thing.

[CDG]

There's a few reasons why light fuses blow:
1. The connectors/wires are loose, corroded or shorted. bulbs, relay, etc
2. one or both bulbs are defective
3. the switch is defective, but not for our SVX's, cause the switch drives a relay.
4. the relay is defective
5. voltage is too low, so current goes up.

my guess is gonna be #5.
when you add the foglights to all the other lights you cause the draw on the system to increase by a lot, if your battery is not 100%, or the connection to/from it are not 100%, then you could effectively be drawing more current, therefore causing the foglight circuit to drawing more than it should.

So how do you fix this?
search the forum for the battery or ground wiring upgrade.
start here, if you've got it already, then start at #1, and if you get to #5 again, check #5 thoroughly.

[gl1674]

5. voltage is too low, so current goes up.

Voltage goes down, current goes down. Voltage goes up,
current goes up. Ohm's law.

[CDG]

Originally posted by gl1674


Voltage goes down, current goes down. Voltage goes up,
current goes up. Ohm's law.

hehe you're absolutely correct, sorry.

Anyways, the fact is that the Battery wire upgrade removes the extra resistance in the system that causes insuficient current and voltage to flow.

#5 should have read:
wiring resistance goes up, so current goes up

[benebob]

Or you could simply clean your ground connectors. I'm on my 7th subie and have never had a grounding problem that so many speak of but then again I try to keep everything clean under the hood. That's not my problem though. I think I have a broken wire as the fuse blows when you put a new one in with no power going to the fogs.

[CDG]

Right, if it blow right away, you have a wiring fault.
put a volt meter on the 2 fuse connections. start poking around till you see a change.
with what you explain, the fuse supplies power and the other end is grounded somewhere. Pull the bulb sockets one at a time. obviously if you remove the bulbs the voltmeter should drop to zero, if not you have a short before the bulds.
I think you can figure it out. Its the finding the short to ground that'll be the Biatch.

Yoda, if your's blows right away, same thing, if not, start cleaning all the contacts.

[UberRoo]

Frequently on bulbs such as the type used in the fog lights, the single wire that runs to the center of the bulb becomes grounded. For whatever reason, these bulbs are of the cheapest manufacturer and become grounded for any of several reasons. The most common ground is that the metal post coming out of the bulb to which the wire is crimped gets bent and touches the metal case. Second, the insulator on the other end of the wire where it plugs into the harness is too small or slips out of place and the wire rattles around until it grounds. Third, the insulation on the wire itself frays, or wears, or melts, or is trimmed too short, or is actually conductive itself. I swear that as stupid as all those reasons sound, I've seen them all happen.

If your car predictably blows fuses, remove both bulbs but leave them attached to the wiring harness, set them on a towel (so they can't touch a source of ground) and turn on the fog lights. The lights will not come on, but the fuse shouldn't blow either. If the fuse blows, you've got a problem hidden somewhere in the harness. That sucks. If it doesn't blow, plug one light in (while the lights are still turned on) and see what happens. Check to see if it blows a fuse immediately. If it does the bulb assembly itself is bad. Again, with only one bulb at a time, try this with the other one.

If your car blows fuses kind of randomly, check each bulb very carefully for ways the wire could ground itself. (I've often wrapped the wire in electrical tape or shrink tubing, but some assemblies are small and will melt plastics, so I've resorted to scraps of fiberglass.) If a source of ground in the bulb seems dubious, simply unplug the bulb completely and drive around this way for a while and see if the fuse blows. Remember that the best way to troubleshoot is to remove all possible causes, and then put them back one at a time. (Remove both bulbs, put one in at a time.) Intermittent electrical problems will require patience.

Option Tancred = Put a 20 fuse in their and not a 15...Its works, stopped blowing..hehe...

[Yoda3000]

Bad bulb?

I did the reccomended tests. Thank you SOOO much for your help. Well I got them to the point both were back in and at that point one of the bulbs wasn't on. I took it back out and the filament in the bulb was fine, it was just completely disconnected at BOTH ends. That's right, i am sitting here holding a bulb with a perfectly good filament loose inside it like a rattle. I think these are the old bulbs that came with the car.

Have a look.

Anyway, no blown fuses and i think if i get a new bulb they'll both work fine. could a bad bulb cause the fuses to blow?

Again, thanks for the help.

[UberRoo]

Yoda3000,
Haha! I've never seen that before. I'd, uh, say you had a bad bulb.

I suppose there's an offhand chance that a bad bulb could eat fuses. Maybe the filament is wrong - it did come loose after all. This suggests to me that the bulb is of substandard quality and may certainly be the source of your problems. Normally, a bad bulb will not blow fuses - but I don't mean bad in the same way your bulb was bad. Too large of a bulb can blow fuses, but not a bulb of factory wattage.

tancred,
Putting a larger fuse in can sometimes solve a problem, but you're not fixing the problem, you're covering up the symptom. If you use higher wattage bulbs, you may need to put in a larger fuse, but be aware that the factory wiring was not designed to handle a larger load. Usually everything is overbuilt enough that this isn't a problem, however, I wouldn't put a fuse in that's more than one size larger. If the factory fuse is a 15, and you blow 20s, you've got bigger problems that need to be addressed before you set your car on fire.

Im not poping 20s or 15s, I just happened upon a blown fuse, so all i had was 20 and droppd it in...

BUt the previous owner somehow blew the 15...