20 amp fuse instead of a 15 amp fuse

I have a short somewhere in the wiring for my power locks that keeps blowing the 15 amp fuse. I can’t find the short, so I just put in a 20 amp fuse instead. So far it’s working. The locks work fine and the fuse hasn’t blown again since. Do you think that 20 amp fuse is dangerous in there? I mean, is my car going to catch on fire now?

Of course it’s dangerous. The wiring is rated to handle 15 amps and you’re letting 20 amps go through it. A fire is certainly possible here.

You more likely have an overload. If you had a short circuit, it would open a 20 amp fuse as well. I would do what you did but would keep a wary nose open for odors of warm insulation. If you don’t see or smell fire in the next 6 months or so, my guess is that you are good to go.

A far out guess is that one of the door lock/unlock solenoids may have shorted turns in the coil but with added current to fewer turns still provides enough amp-turns to operate the solenoid. If this is the case, the solenoid may eventually fail completely with or without a fire and more likely without in my opinion.

Have you ever seen a car with the interior on fire. It’s something to see and feel from a great distance. Don’t park this car anywhere near your house, any other house or building, any other car, or anything else. It would also be best if you didn’t drive it.

I’d remove the fuse, fix the problem, and put a 15A fuse back in, in that order.

If not a fire, you’ll have melted wires soon and THEN you’ll have a short.
At least you’ll know which lock solenoid was the culprit.

The thing that’s a little scary here is that the power lock circuit is ‘hot’ even with the key off. So if you do have a problem, it could develop into a real catastrophe at any time of day or night. Personally I don’t think the extra 5 amps will make that much difference—a direct short will still blow a 20A fuse mighty quick!

Does the fuse blow only when you use the lock, or do you just notice that it doesn’t work? Also, when you look at the blown fuse, is it just melted, or does it look like a tiny firecracker has gone off inside it? If it’s just melted, you have an overload. If it looks like it really BLEW, then you have an intermittent direct short somewhere.

Definitely keep an eye on it.

You didn’t say the year of the vehicle, but one thing common to older vehicles is that the insulation on wires in the wiring harness that ges through the holes in the body and door becomes chafed and cracked and shorts out. You may have a high-resistance short to ground. That’s a short but not a “dead short”.

The harness to the driver’s door is the usual suspect, becaus thet gets flexed repeatedly every tim ethe car is used.

These types of shorts can often be found by removing the door panel, untying and “breaking into” the harness, seperating the individual wires, and checking continuity (in this case to ground) while flexing them. You’ll want to have the battery disconnected when you do this, as the lock circuits are always “hot” even when the key is out. Sometimes the cracks and chafs can be visually seen on the wire insulation.

There is a Hypot (high-potential breakdown) test that can be run, but you probably won’t need to go that far.

PS: I agree that the 20 amp fuse is a bad idea.

The locks will work for about a day with a 15 amp fuse, and then I’ll just notice they no longer work. When I pull the fuse, it looks like a fire cracker went off inside- all black. So I took the door panel off to see if maybe a wire was exposed, but I couldn’t see anything. I removed the 20 amp fuse for now after seeing these posts, but it’s been working for a good week now without a problem.

“The locks will work for about a day with a 15 amp fuse” – Sounds like something intermittent.

“it looks like a fire cracker went off inside- all black” – Sounds like a short circuit to ground. (And, as Wha Who said, that would blow a 20A fuse, too.)

“and then I’ll just notice they no longer work” – If the fuse blows without your operating the locks (i.e., it happens all by itself) then the problem is on the “hot” side of the wiring, between the fuse and the switch(es) or solenoid(s), whichever is connected to the fuse.

Good luck tracing this down. (I hate intermittents.)

yes 20 amp fuse instead of a 15 amp could cause a small BBQ

When a fuse blows, there is a reason. A direct short circuit would blow either a 15 ampere or a 20 ampere fuse immediately. However, when you put in a 20 ampere fuse, and it doesn’t blow, while a 15 ampere fuse does blow, you are pulling more current through the wires than the wires were intended to carry. This leads to heat, melted insulation and a possible fire. On a fused circuit, a dead short rarely causes a fire. However, pulling more current (amperes) on an overfused circuit (using a 20 ampere when a 15 ampere is required) sets up the conditions for a fire whether it is in a car or in a house.
I bought a new Ford Tempo in 1985. I had only had the car a month when the fuse blew for the tail lights. The dash lights were on the same circuit so I knew when the fuse blew. A replacement fuse would last up to a week and then would blow. The car was on warranty, so I took it back to the dealer. The problem turned out to be that some Ford Tempo models were equipped with a tail light monitor. This monitor circuit had a very thin wire leading back from the tail lights. My Tempo didn’t have this feature. A goof at the factory had this thin wire powering the tail lights. The insulation melted off this wire and when it touched the body of the car, the fuse would blow. The service technician thought I was fortunate not to have had a fire in the trunk. At any rate, the proper wire was connected and the problem was solved.

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