Coil wire burns when engine stops

[YY1]

I toyed around with my recently acquired 73 over the weekend, trying to see if it would run. The dash harness, column and pretty much everything else in that area are out, and the engine harnesses are dangling from most things.

I put in a battery, attached a remote starter switch, and jumped the + side of the coil to the battery.

It acted like it wanted to go from the first try, and after several attepmts, ran on it's own for about 7 revolutions, then died. When it died, the jumper from the coil to the battery caught on fire, and burned up. I tried it again with a new jumper and the same thing happened.

The jumper is about 20 ga, and I think the factory is like 18. Is this just too small, or is there a problem somewhere? ballast resistor, maybe?

I ran my 70 Bee for about a month using an 18 ga jumper on the coil, while I tried to figure out what was eventually discovered to be a bad bulkhead connector. It never burned up the wire and I drove it every day.

 

[70rr-brian]

Well correct me if I am wrong but I think the intial voltage to the coil should be about 12v (which is actually close to 9-10 volts if you factor in the drain on the battery during cranking at startup) then once it starts running the ballast resistor should reduce it to the 5.5v range.

Perhaps when it did its 7 revolutions it kept getting full voltage and overheated the coil and it manifested itself in a burnt wire. Just a guess.

Try a different grounded ballast would be where I would start since they don't cost much and you probably have some spares laying around.

 

[74sundance]

Well correct me if I am wrong but I think the intial voltage to the coil should be about 12v (which is actually close to 9-10 volts if you factor in the drain on the battery during cranking at startup) then once it starts running the ballast resistor should reduce it to the 5.5v range.

Perhaps when it did its 7 revolutions it kept getting full voltage and overheated the coil and it manifested itself in a burnt wire. Just a guess.

Try a different grounded ballast would be where I would start since they don't cost much and you probably have some spares laying around.

You got it right!

 

[YY1]

Ballast resistor was actually the first thing that popped into my head.

What part is grounded? It looks like the bolt to the firewall goes right through the ceramic.

Wonder why my old Bee never burnt the jumper?

Unless the ballast on the 73 is bad? ...but I bypassed it on both cars...or so I thought.

I also thought tha the voltage was for cranking, and got reduced after starting.
Wouldn't that cause the wire to burn after the starter disengaged, and not after the engine died?

 

[Ron 73]

The bolt does go thru the ballast resister, Brian's right when you turn the key to crank position it should have 12 v to it when you leave off the key it returns if i remember to 7 volts. With a 12 volt test light, not meter you can check the voltage drop if the light is bright in cranking position starting, and dims when you turn back to run then its ok. If you by pass it on a points system it could burn the points up so it could be the problem, that is a quick way to see if its working right though. I know of no grounding with these unless its in the wiring itself because the bolt goes straight thru the porcelain to firewall unless theres a metal clip in that hole bolt goes thru. Constant voltage in excess could cause the wire to burn. Good luck.. I think its the pink wire on it that powers the + side of coil, not positive with that.

 

[Ron 73]

Here is a test to check coil if it helps..

This testing procedure is valid for just about any automotive coil. Using an ohmmeter, check the resistance between the side terminals of the coil. Do this with all of the wires to the coil disconnected. You should see 0.75 to 0.81 ohm of resistance. Then check the resistance between either side terminal and the center high tension terminal. The reading should be 10,000 to 11,000 ohms. Any significant deviation from these numbers would indicate that the coil is defective

 

[70rr-brian]

Your right...there is no ground on those I was on crack.

 

[YY1]

I think I'll try jumping the battery to the ballast, rather than straight to the coil, if I can trace it out. Will also look for a spare ballast resistor.

Maybe my balast was still in play back on the Bee, because the rest of the harness was stil there, even though I went from a 12v at the bulkhead, straight to the coil.

Thanks for the help

 

[Histoy]

It's possible that your jumper wire was too small to carry the load once your engine died. If the ignition points happened to be in the closed position, it would provide a dead short from the battery to ground.

 

[YY1]

It's electronic- no points in 73.

I tried to make a 16 ga jumper today, but I can't find my good iron, and the one I could find is making cold solder joints.

Looked like rain, too, but never did. Hate to take off the tarp if rain is threatening.
Did start to build a battery tray, though.

 

[YY1]

Just a staus update. I found my good iron, and made a 16 ga jumper. I jumped the ballast rather than the coil, and one of those two changes (or both) worked.

It ran on it's own fuel pump today for as long as I held the throttle open, but wouldn't idle. I did find some more areas of open vacuum port style issues to address, though.

I'm claiming progress.

 

[74sundance]

Just a staus update. I found my good iron, and made a 16 ga jumper. I jumped the ballast rather than the coil, and one of those two changes (or both) worked.

It ran on it's own fuel pump today for as long as I held the throttle open, but wouldn't idle. I did find some more areas of open vacuum port style issues to address, though.

I'm claiming progress.

Cool good for you!! Keep us posted and let's see some pic's