Fuse instead of fusable link blows while driving.

[TCLARK]

The fuse of my Frankenstien started blowing while driving and truck. I put in another 30 fuse and starts right up. I'ts an I6 converted to V8 with HEI. Been my daily driver for years like this. Just started blowing fuses. Put new Voltage Regulator on, same thing. Had Alternator checked, OK. Getting ready to put '67 body on this '72 frame with new wiring harness in the near future. Do want to put new harness on the old body right now. This wiring is scary, but it's been working for years like this.Any help appreciated !

[LockDoc]

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Has it been draining your battery at all when it sits?

That would have to be a pretty substantial short to blow a 30 amp fuse. I'm not sure if the alternator could be shorted inside and still test good or not. I would follow the main power wire across the core support to the junction where it connects to the other two red wires and make sure it isn't shorted out there somewhere.

LockDoc

[TCLARK]

Originally Posted by LockDoc

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Has it been draining your battery at all when it sits?

That would have to be a pretty substantial short to blow a 30 amp fuse. I'm not sure if the alternator could be shorted inside and still test good or not. I would follow the main power wire across the core support to the junction where it connects to the other two red wires and make sure it isn't shorted out there somewhere.

LockDoc

If it sits about a week it will. I disconnect the battery when I'm not driving it, too hot to drive, no AC. I thought it was the Alternator, tested good. May switch it out with another.

[cj847]

Where is your fuse? Is it in the position where the fuse link was?

I will assume that is the case. If the 30 amp blows before any of your fuse box fuses, that seems to indicate that the short has to be under hood.

It is odd that it slowly drains your battery, then blows a 30 amp fuse. That sounds like two different problems to me.

All I would recommend is similar to Lockdoc. Trace all of your large wires and look for ways they can wiggle and short. Also check horn relay and circuit.

[TCLARK]

Originally Posted by cj847

Where is your fuse? Is it in the position where the fuse link was?

I will assume that is the case. If the 30 amp blows before any of your fuse box fuses, that seems to indicate that the short has to be under hood.

It is odd that it slowly drains your battery, then blows a 30 amp fuse. That sounds like two different problems to me.

All I would recommend is similar to Lockdoc. Trace all of your large wires and look for ways they can wiggle and short. Also check horn relay and circuit.

Yes, located in same place.Don't think Battery & fuse blowing are related. Before it might blow the fuse once in a while.

So, no short under the dash would make the fuse blow ?

[truckster]

It's not necessarily a short. If the amperage draw on the circuit exceeds the rated amperage of the fuse, the fuse will blow. Does it blow immediately when you start the truck, or does it take a while? What happens if you run the truck with all accessories turned off? What if you have the ignition on with the engine off? There's more to explore here...

[TCLARK]

Originally Posted by truckster

It's not necessarily a short. If the amperage draw on the circuit exceeds the rated amperage of the fuse, the fuse will blow. Does it blow immediately when you start the truck, or does it take a while? What happens if you run the truck with all accessories turned off? What if you have the ignition on with the engine off? There's more to explore here...

If runs fine when to start it, I can drive around. Once I turn it off, nothing. Until I put in new fuse. Only thing I've done recently is New Grant Steering wheel, horn is screwed up.

[truckster]

What happens if you turn the key on (without starting) and then turn it off? Does it blow the fuse? You might have a short in your ignition switch.

[Sheepdip]

Originally Posted by truckster

What happens if you turn the key on (without starting) and then turn it off? Does it blow the fuse? You might have a short in your ignition switch.

^^^^^^^^^^^^Good Answer^^^^^^^^^^^^^

[RichardJ]

>> Been my daily driver for years like this. Just started blowing fuses <<

Are you saying you put the fuse in years ago? Why? You had a problem years ago and you didn't fix it then? Why ? A fuse is a poor substitute for the original fusible link.

>> I disconnect the battery when I'm not driving it << Why? What prompted you to start doing that?

>>Only thing I've done recently is New Grant Steering wheel, horn is screwed up.<<

Did the fuse start blowing or the battery dying or both when you changed the steering wheel ?

[mr48chev]

By all rights and regulations you should loose all power When the fuse blows when you are running down the road. Meaning that the truck has to be running off the alternator after it blows.

That means that the wire shorting out via vibration would be a pretty viable candidate. I'd check the main power feed lines from the fuse link to alternator, regulator and firewall connection plus the second wire that is hooked to the

You should be able to track the wires with this diagram. I'd especially check where it runs along the core support and crosses back down to the regulator on the drives side.

[TCLARK]

Originally Posted by RichardJ

>> Been my daily driver for years like this. Just started blowing fuses <<

Are you saying you put the fuse in years ago? Bought it that way. Why? You had a problem years ago and you didn't fix it then? It just started.Why ? A fuse is a poor substitute for the original fusible link.

>> I disconnect the battery when I'm not driving it << Why? What prompted you to start doing that? Got tired of jumping it off when it sat like a week.

>>Only thing I've done recently is New Grant Steering wheel, horn is screwed up.<<

Did the fuse start blowing or the battery dying or both when you changed the steering wheel ?

Not the battery thing.

[mr48chev]

In the simplest terms, fuses only below because something down stream from the fuse is drawing more amps than the fuse can carry. The fuse is the sacrificial piece = the intentional weak link in the chain.

The battery cannot cause it to blow. Having a big spark at the battery from the jumper cables being connected wrong once can blow a diode that may be letting the battery drain though.

Parasitic drain= something that draws just enough amps to drain the battery over a period of time.
Examples: Dirty battery top that lets current flow across the battery to ground.
Glove box or other light that stays on when it shouldn't.
Electronic device that stays on and draws power.
Blown diode in alternator. Very common on rigs that have been jumped a
lot.


Items that often blow fuses.
Direct or intermittent short in wiring. It's not a full time direct short because the fuse doesn't blow the minute you put it in it blows when you are driving the truck. That would be an intermittent short caused by a wire wiggling around or the end of a wire flopping around because a hot lead was disconnected and left dangling where the end could short out. Or a wire has a bare spot that makes contact under certain conditions such as bouncing down a rough driveway.

Shorted accessory.
Simply an electrical item on the truck that has failed electrically inside and is shorted inside. Since the horn doesn't work and evidently hasn't worked when you put the horn kit in did you hook up all the pieces? Could it be that you are bumping the horn button when you drive and causing the horn circuit to go to ground blowing your main fuse? It should blow the horn fuse but has somone bypassed the horn fuse?

Other accessories or electrical units that just flat draw more amps than the fuse will handle.

Big amp for the sound system?
Speaking of sound systems, one of my students used to leave his Impala lowrider parked at home when he went to work at night because he didn't want it banged up in the store parking lot where he worked. Battery would go dead a couple of nights a week and he would have to jump it to get to school in the morning. We ran every electrical test in the book and there were no issues with it. Come to find out that after he left for work his 12 year old brother and his buddies would turn the sound system on and play it until the battery drained down while he was at work. His mom finally mentioned that they were doing that.
High power halogen headlights or driving lights. Had a buddy who put KC daylighters on his 4x4 a number of years ago and had the battery go dead when he was running around in the hills because the lights drew more amps than the alternator charged. He had them hooked up right with a relay and all but the alternator couldn't keep up with the draw of all of his lights. Hooked up direct they might draw more power than the fuse will handle. The halogens in my 71 drew so many amps that I was burning up dimmer switches every few months until I installed relays for the lights.

[TCLARK]

Mystery solved....Bad Alternator ( that checked out good at AutoZone )..