Coil/ Ballast resistor question

[Desert Rat]

After a couple of frustrating hot no- starts and scouring the forums, I think I may need a new ignition coil. A bit of reading here had me going in the direction of a Pertronix coil but a call to them for an exact part led to them telling me they don't make a coil for my car because they contain internal resistors. Looking through my books and wiring diagrams, I don't see anything about a ballast resistor or see anything wired in the engine compartment that looks like one. 

Question is can I just swap out this old oil filled coil with a new 6 v Pos grd coil or should I be running a ballast resistor, or do I need an entirely different  coil?   

 

1937 P4 Plymouth coupe

1954 218 Plymouth engine

6V/ Pos ground

Points

Existing firewall mount coil Echlin IC-7   1.2 ohms primary resistance

[Los_Control]

The ballast resistor comes into play when you have 12V electrics.

The job of the ballast resistor is to drop the voltage from 12V to 6V so the points will last longer.

Mopar even kept the same ballast resistor system into the 70's with electronic ignition just to keep it easy on the electrical components.

 

Since you are 6V, you just need a regular 6V coil. .... Here is a photo of my old 12V coil.

 

All this means, it is a 6V coil and it is expecting you to drop the voltage to 6V with a external ballast resistor before the coil.

A coil with internal resistor will accept 12V and drop it to 6V going through the coil.

 

So a 6V car does not need to be concerned with a ballast resistor. .... Only Mopar used the external ballast resistor and it does not make sense to me.

Chebby or Ferd never used a ballast resistor .... Sorry for the rant.

I switched to 12V, electronic ignition with a GM control module and petronix coil because it makes sense .... too me.

 

I should add, a new coil does not care which polarity you run through it ... positive ground is fine on any new coil. It does not care.

If you have a old coil with 50K miles on it, it might complain if you swap polarity on it and give strange problems at different RPM's

 

 

 

Edited January 22 by Los_Control

[kencombs]

I don't understand why one would source a coil from petronics if you have a points ignition.    Any quality stock replacement is fine.

 

As to the ballast resistor and their comments, I really doubt the competency of the tech guy as there are no coils with built-in resistors. ** There is a lot of discussion on them but what they really are is different number and gauge of windings, not another component.   And as far I know Chrysler never used them or ballast resistors on 6v cars.   

 

**

The exception to that rule was a few temperature resisted coils used on a few mid 50s Mopar 12V cars.  I've only seen a couple of these, a thermistor located in a little compartment on the bottom of an otherwise stock appearing coil.

 

In any case, before condemning the coil get yourself a spark checker to insert in  the coil or plug wire and be sure of the lack or presence of a spark when it misbehaves.

Edited January 23 by kencombs

[clarkede]

18 hours ago, Desert Rat said:

After a couple of frustrating hot no- starts

Could your "hot no-starts" be a result of "vapor lock"?  Might be a fuel supply problem.  I've had this problem where the car starts cold and runs fine, however, after turning off the engine and letting it sit for a few minutes, the engine will then not restart.  Many on the forum users have installed electronic fuel pumps (either in parallel or in-line with the mechanical fuel pump) to help solve this problem.  Before installing an electronic fuel pump, I've attempted to insulate my fuel supply lines near the exhaust system to help prevent the vaporization of the fuel, but that doesn't completely eliminate the issue of the fuel in the carburetor bowl vaporizing.

 

I remember having this problem when I drove the car a lot when I was younger and I would carry a can of "starting fluid" with me.  When it would vapor lock, I would just shoot a little down the carb and it would start right up.  To troubleshoot your hot start issue, you might try something like this the next time it acts up to see if it is your coil or fuel.

[Desert Rat]

I can say I have seen the vapor lock issue before during the summer when the car was under more extreme conditions. I put in a heat shield and that seemed to help a little bit. But these other times seemed different. Two of these no start incidents were in cooler weather only about 10 minutes or less into the drive. I tried the squirt of starting fluid even after waiting about 5-10 minutes for things to cool and settle, still no start. 

The spark plug checker is a great idea though. I picked up a new coil from NAPA yesterday but I'll bring my plug checker along if it happens again. 

Thanks for the input on the resistor. Just wanted some feedback to make sure I didn't have the wrong coil or a missing part from PO possibly. 

[Sniper]

Might see how hot the coil is during these no starts compared to times it starts fine.

 

Had an issue years ago with my 87 Diplomat dying when hot, let it cool and it started/ran fine.  In this case the coil was located fairly close to the pre cat on the fender well.  A new coil, relocated to the more traditional spot on the intake of the 360 and no more issues.