Fuse Keeps Breaking

[McCluskey]

I've had an issue that has become much worse lately. The 20amp fuse for "Engine Compartment" the fuse that functions the Glowplug system, Fuel Gauge, Parking Light, etc. It has blown a few times in the past at random. Now it always blows new fuses upon initial start up. I hooked up a volt meter to it, but I do not see any high numbers. One time I thought it may have read 65V, but I think it may have been mistaken. It hovers around 12v +/- when its on Run, Start. I tried jumping the circuit with some wire and everything functions, all lights and devices. I cannot track down why the fuse keeps blowing.

 

[MarcusOReallyus]

You don't need to see high voltage to blow a fuse. In fact, that's not usually the reason. Can happen, but that's not the prime suspect.



Excessive load (in some form) is the prime suspect. That excessive load can come in many forms. A short circuit, or partial short circuit from frayed wiring is a common way. It can be a device that is going bad and drawing too much current. Functionally, that's the same as a partial short.


In fact, you're more likely to see LOW voltage on a circuit just before the fuse blows. But you aren't likely going to see it with a standard voltmeter. It's there and gone too fast to register.

So, start isolating components. Identify everything that is powered through that fuse, and start investigating each one.

 

[KsM715]

Voltage usually doesnt blow fuses. Its the amps. There is something wrong in that circuit causing it to blow. A fuse is a protection device. You need to find out what is shorting out or causing a high amp draw in that circuit.

 

[whatadeuce]

Do you have a wiring diagram for this vehicle? awhat vehicle is it?

 

[eagle4g63]

I'm figuring the blazer he has listed in the sig line................and from the glow plug comment.

Anyway, if you can take out (temporarily) one system at a time from that circuit and see if it does it, if not than you know what system to start looking at.

 

[whatadeuce]

Hello eagle4g63, Thats the reasoning I would suggest as a start...

 

[Goose2448]

You haven't added anything to the truck have you?

I know I added a radio to my civy C20 and started blowing my running lights fuse. Blew both tag lights, and the fuse. Being young and dumb, 17 at the time, I just up the fuse from 15 to 20 amps. No more problems with that. I figured with the addition of the newer radio and the extra lights on it drew more amps.

 

[McCluskey]

Wow, I goofed. Sorry guys, this is my 1986 M1009 CUCV.

The only thing electrical I've added to the truck is a 12V cluster which has been wired in for quite some time, long before I ever started blowing these fuses.

Yes, I have all my TMs for the truck but I'm still at a loss. I trace through, what I believe, are all the associated circuits and cannot find any obvious problems.

 

[ARYankee]

Does it blow while the glow plugs are cycling during your wait time to start it?

 

[McCluskey]

I'm not exactly sure when its blowing. I know a few times it blew before the wait light came on. I'm out of 20 amps now, so tomorrow or Monday I need to go get more.

 

[24farragut]

did you ever figure this issue out? happening to me all the time.