blown fuse problem

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keyswitch1

Senior Member
How do you find out why the fuse blew ?? As soon as you put a new fuse in and turn the key on it blows Thank you in advance !!
 
Good afternoon...I believe that you have developed a short. Start at the battery and trace your wiring system and see where the problem is. Go step by step with a test light or a metre and see what you can find. The last one that I traced was a loose crimp on the back of an Amp Meter...another was the actual fuse holder had become loose at the rivet and shorted. Good Luck...Ernie in Arizona
 
You'll have to disconnect circuits to stop it. Is it really as you turn the key, or do you have your foot on the brake as is a normal thing to do? Turning the key only and it blows...I'll defer to the experts.

My experience has been bad stop light switches twice. Took the wires off the switch no more blown fuse.
 
What size fuse are you using? Common causes would be bare wires shorting. If the fuse blows when you turn on the key you know it is in that circuit. Good luck.

Charlie Stephens
 
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Take off the battery ground cable. Connect a test light or volt meter to that cable end and the battery post. Turn the key on. The light should light or meter should meter. Keep disconnecting things electrical until the light or meter go out and stop reading the draw,,, thats your problem.
 
If the fuse isn’t blowing until you turn on the key, than I would say the problems is after that. In the ignition side.

You should be able to rule out anything before ignition switch. Should not be hard to find. Check wire in distributor, etc.

Good luck.
 
Could be lots of things, but if your wiriing is in a metal conduit make sure the conduit has not moved and is making contact inside the terminal box with the driver's side post.
 
Had an issue with my car everytime I turned on the headlights the fuse would blow I pulled the conduit and the original harness was cut and spliced and shorted to the inside of the conduit so I put a new harness and everything is good now no shorts
 
With the original pop out switch, you can turn on the key and nothing is even hot yet if the points are open since the switch was in the breaker side of the circuit. No telling how it's wired now.
 
So you had a box of defective fuses ?

I'm thinking you might have gone to a heavier fuse which means there may still be an issue unless the other fuses were too light.
 
A good thing to remember is that fuses are there to protect the wire. Each wire size (American wire gauge) will use a different size fuse. A 10 gauge wire will handle 30-amps. If it's any smaller than that, a person would need a smaller fuse. 12 gauge would be 20-amp and 14 gauge would be 15-amp. A lot of 6-volt stuff in only 16-gauge and the proper size fuse for that is a 10-amp fuse. You can use smaller fuses for each size if you wish but you shouldn't use larger sizes. Under a short to ground condition, the wire can catch fire before the fuse blows if a person doesn't size it right. I've seen it happen and it burns quick.
 
keyswitch1 said:
I put a 20 amp fuse in. Is that OK ?
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A 20 Amp fuse is under the 30 AMP rating so it is "safer" but you may exceed the rating and burn the fuse. IF you do not burn the fuse with all your lights on during maximum amperage draw then a 20 AMP will work; if you burn the fuse then increase to the 30 AMP rated fuse.


NEVER go above the 30 AMP fuse or you will damage the wiring in the car and may start an electrical fire which can destroy your car...
 
20A is appropriate to the 12 AWG wire between battery and generator and will handle the draw of the original lighting system. 50CP bulbs may give you a problem. Most guys use a 30A fuse because, you know, nobody's seen those wires in flames, have they?
 
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