Burning up coil fuses

It's bad enough when you have to call your wife to come get you because the Jeep quit. It's really bad when she picks you up, you go home to get the tow equipment... go back to the Jeep and realize you brought the tow bar but not the ball and mount for the truck and have to go home AGAIN for it :evil:
It's EXTREMELY bad when your wife falls down helping to push the junk, getting multiple scrapes and contusions, and certain she was going to be crushed by the Jeep (she wasn't, I had it)

(Doug, this wasn't quite as bad as Kent's situation... but close enough!!)

Then riding home with the Jeep in tow and no ballast in the truck, so it was noticeable when it swayed a bit on the highway... she was sure someone was going to be killed...



She insisted I get rid of it and go get a new Jeep...

So here's the history:
Saturday I installed the new Pertronix. It's identical to the old one.
I cut the red and black wires that were already installed, spliced the new ones onto those, solered and taped them.
I did route the wires slightly different under the cap, ran them through a hole in the plate that holds the vac advance.

It started and idled fine, then died after ~10 minutes.
I rebuilt the carb, tried to start, then found the blown 30A coil fuse. Replaced it, ran fine around the block Sunday nite.

Last night, I ran it 10 miles to the electrical supply store. It died at 9 miles, in the tiurning lane of a 4-lane highway. I checked the coil fuse, blown. Replaced it, got off the highway. 2 more fuses blown in the next mile... I got to the store 5 minutes before it closed. Bought my item, called home for rescue.
Popped the hood while waiting. The coil was HOT.
I had installed a new replacement coil, cheapie for ~$12 that I had as a spare. I suspected maybe it had the wrong resistance, so when I returned (the first time) I installed the Jacobs coil I had run with this set up for ~ 8 years. Tried that with my last fuse. Got about 150 yards, it blew the last fuse.
That was it, out of fuses and ideas I towed the junk home.
In strained silence and a few tears, see above.

OK so what is causing the 30A fuse to blow? Why is the coil getting hot?

Not a dead short, because it will run for awhile with a new fuse, or so it seemed... when it's not hot (note installing the other, cold coil and blowing another fuse within a minute or two seems to negate that theory )

I am running the ballast resistor with the Pertronix. Directions said if you had one before, leave it in. I ran it that way for years with the previous unit.
Bad ballast resistor?
Shouldn't really matter, the Pertronix should run OK on 12 V and not affect the coil.
None of the other wiring was changed.

I guess I need a lesson on coil theory and operation/troubleshooting.
I'll go search now... but feel free to post your thoughts.

 

Wow, glad your wife is ok, didn't get hurt worse. How long is the wire that's in line with the fuse? What gauge is it? Bad wire, bad insulation, rubbed somewhere that you don't see?

 

The fuse is in the Painless fuse block. Most of the wires are in plastic loom with zip ties and/or tape. Rubbing/insulation wear isn't likely. The wire from the Pertronix back to the wire in the harness is the length of the engine block. That wire does have two soldered splices, one old, one new. Wire gage is probably 14, as supplied with the Pertronix.
ThePertronix wire that goes to the coil neg. has one new splice, soldered and taped.
I guess I can check the new splices I made... even though they are soldered ,maybe something is amiss... could a bad/weak connection in one of these cause the coil to get hot and blow the fuse?

As for my wife's fall, thanks... a few small bumps and scratches, scared her more than anything.

 

Maybe I'm missing something here, but I believe 14 gauge wire should have melted the insulation and caught on fire if enough current went through it to blow a 30 amp fuse.

 

Those wires, coming out of the Pertronix, really shouldn't have anything to do with it, unless a bad connection is causing the coil to heat up and draw more amps to function.

Looking at my Painless diagram, system power goes from the starter solenoid to the fuse block. from there, a wire comes out of the fuse block, through the BR, and to coil +.
In addition. I see there is another wire identified as coil from the fuse panel to the ignition switch...

Glenn, 14 ga shows correct in the Painless instructions.

 

I'm going to give Painless tech a call, see which side of the coil circuit has the fuse. Maybe it's a bad connection, dirt, etc, in the ignition switch side....
Painless opens in about 5 minutes.

Russ....

 

Painless said the fuse is after the ignition switch.
Said it sounds like the coil is going bad... but this happens with 2 different coils, after it gets hot.

As said, a dead short would pop the fuse immediately, not after the engine gets hot.

The likely culprit then is the ballast resistor.
If the resistance is too high, causing low voltage to the coil, the coil will overheat because it's trying to do too much work with not enough voltage... draws more amps, pops the fuse.
I'll put a meter across the BR and see what I get. Painless said 1.15-1.3 V drop across the BR.

The good news is that BRs are cheap.
I need a bunch of 30A fuses too. I had 3 spares, burnt them up as well as the ones I canabalized from the headlight circuit and the heater circuit...

 

Given that I know nothing of electrical theory...
I think I should have said 1.15-1.3 ohms drop across the BR.


My understanding of a BR is that it drops voltage for power to the coil in the 'run' circuit from 12V to somewhere between 6 and 8, thus preserving points (in systems so equipped) and generally extending the life of the coil.
So I should be able to measure the resistance across the BR terminals, correct? I believe if I'm getting more than about 1.3 ohms resistance, then that translates to reduced voltage to the coil to an unacceptable level. In turn the coil draws more amperage until it zaps the fuse.
:?

If I'm off base here... feel free to set me straight!

(Thanks for the sensitivity regarding my wife I showed her Russ's post above, I think she felt a little better knowing others go through this. It's really a new experience for her, this CJ stranded me only one other time over the years. The big black mark in her mental "book" will last alot longer than her black-and-blue marks, I'm afraid... )

 

Thanks Mike. I'll let you know... prolly easiest to stop by FLAPS tonight and see what they have, since I'll be there for a bunch of fuses anyway
If I strike out I'll get back to you.