Melted fuse holder

Isn't the fuse supposed to bust before the wiring melts the holder? I left my lights on the other day, ended up with a dead battery which was no big deal being parked on a hill. But when I went to turn on the headlights they were beyond dead. I have an in-line fuse hooked up to the switch and the fuse holder had melted. I'm not even sure what fuse was in there at this point.

Why would it do that?

An overly large amp rating on a fuse would allow too much current to flow, causing accumlated heat buildup in a plastic fuse holder that was probably made in China?

Is it possible that a previous owner put the proverbial penny into the fuse box to solve some undiagnosed problem?

What kind of headlights do you have, Mike?

"An overly large amp rating..."
Voltage rating also. Be sure it says 12v .
Tubular glass fuses come 120v rated too.

I replaced the fuse holder but there's demons in the closet. My mechanic says "no more than 16 amp fuse" but that one popped like a bottle of New Years Champagne. Today I'll have to find the short.

If I take all the connections off the switch and put them back on one-by-one, the shorted one will blow the fuse. How to I test that with a multi-meter so I don't keep blowing fuses?

If you're melting the holder with a higher amperage fuse, then you've either got a resistive short or too much load on that circuit for the wire. I've been in automotive wiring engineering for almost 27 years and I bet on the latter. Has anything been added to that circuit, like driving lights, that weren't originally on it? To answer your question, you can use a multi-meter to measure the load and then determine if that load is too large for the wires that you have servicing it. Fuses are designed to protect wires, not devices. If you increase the size of the fuse, you run the real risk of creating a fire. You're lucky that the damage occurred where it did. It's also quite possible that you have damage elsewhere on the circuit. Increased resistance in the way of corrosion could also be causing the issue. My guess is that some accessory hardware was added at some time that is overloading the circuit.

Tom wrote: "Increased resistance in the way of corrosion could also be causing the issue."

Only because he's seeing something North of a 16 amp load, I would look at something other than corrosion. THAT would be some hefty corrosion, and on a high-current-draw circuit, too! It should show up as a hot spot (high temperature) along one circuit which you could carefully seek out with your fingers.

Continuing: "My guess is that some accessory hardware was added at some time that is overloading the circuit."

That's the most likely, or he has a wire that has become shorted somewhere (like a tight bend around something metalic) but I would put my money on too many things on one circuit/wire. That's a common mistake in home-built/modified cars.

When we built the spyder, the original harness that came with the kit was really low quality. REALLY low quality. The panel was something like 4 or 5 fuses (can't remember, I threw it away) and completely cheesy. When I laid out the harness to figure out what went where, I found FOUR splices in the headlamp harness. On a brand new, rolled up in the box harness.

We pulled the fuse panel from one of the 911's that we were cutting up and used that. Wound up replacing just about every single wire in that harness due to splices. It was like somebody picked up all the scraps from the floor and spliced them together to make the harness, plus they had used pretty small guage wire for the project. The more amperage that you are using, the larger the wire should be.

Not saying THAT's the problem here, but I am quite convinced that had I installed the harness, with the light guage wiring and the splices into the original provided fuse panel, it would have provided interesting failures in the long term...

I should probably add that a 911 fuse panel isn't anything special, it just has good metal in it and it had 9 or so circuits which made isolating circuits very easy.

Our next builds will all have modern harnesses, e.g. Painless, etc. The price is so reasonable on them that it beats making it yourself unless you're an automotive wiring technician for 27 years - LOL - you just whip one up in the garage. The rest of us buy stuff that works 'cause it's like MAGIC!

angela

angela

When I assemble a componet with that may connection I like to put a conductive sealant on it to prevent corsion. I recemend,, Duralco 120 High temp conductive epoxy a product of Cotronics corp.1-718-788-5533.. It helps make things last. and stay grounded One caution it is concuctive put it onlywhere you need it.. It can cause a short If allowed to bridge 2 circuts

That looks like a REALLY good product, Barry. I'll call tomorrow and order some of it. I'm in the middle of an engine swap on a car and I usually go through all the grounds while I've got the car apart. I think this would really be a terrific product for the grounds on the 911 as several of them are in very exposed areas.

Thanks for the info!

angela

Thanks ,I went threw a few products before I found that stuff It's great for grounds and if your careful it can be used on the spade connections you want water proof and tight.. Like a coil wire that keeps slipping off

Their has to be a short on the output of that fuse block or a under sized wire was used. Eather way??? Running a new wire of heaver gauge will fix that..

Also check out the componet it supplies power too.The problem could be at that end of the circut.. A bulb not installed right or a bad socket or a lose ground..

And as always make sure you have oversized and secure mutiple grounding wires. It is a fiberglass car. That should always be over over engineered..

It's the parking lights... or whatever we call the small bulbs inside the headlights. I disconnected those from the light switch and we're good to go. Now I just need to figure out where the short is in that circuit. Thank goodness it's a relatively simple circuit for those two lights.

If the bigger fuse wasn't blowing you do not have a short, but an overload condition caused by either too much load or resistance in the circuit. I would take a look at your ground (as mentioned above) to look for loose or corrosion. A resistive short is possible, but unlikely.

Fuses blow because of to much current. This can be due to:
1.The bulb rated for more current than the fuse.
2. A short (complete or with some resistance) of the hot wire to the bulb.
3. Additional items wired from the same fuse causing to much current draw.

Bad grounds or corrosion should not be the problem. They only increase the resistance in the circuit, causing less current draw.

Problem might be pulse wave modulation...8-)

Pulse THIS, Jim!

I had to refabricate my bulb holders and contacts on the parking lamps

I HAD AFTERMARKET JUNK!! Mine kept flickering and burned up..

But with a scrap peace of copper flat stock from a hobby store and some nylon inner fender wheelwell scraps, and some copper gutter rivits..

I redesigned them into something quite nice. I hope your NOT in that kind of trouble.