View Full Version : Race car wiring

12-06-2008, 10:56 AM
Hello all
I have a 72 Midget for racing (actually two) I've hauled one around for years and it's about 75% finished for vintage. I figured I'd speed the process so I bought an existing racer. Well I'm sorting it out ( nothings ever easy). The previous owner had issues burning up condensers. It's not running an alternator, he has a resister wired between the kill switch and the coil. Could the resister be the problem? I've got a solid state ignitor that I plan to replace the points and condenser with but don't want to fry it if there's an issue. Any ideas

12-06-2008, 11:12 AM
Sounds like a ballast resistor. Under normal conditions, when running the resistor is in circuit and about 8v goes to the coil. For starting only, the resistor is bypassed and full 12+v goes to the coil. It helps guard against starter drain from the battery and provides a boosted spark for starting.
Never heard of one giving condenser problems though.

12-06-2008, 11:32 AM

It's hard to know what "resistor" you are talking about.

Like Roger, I'll assume you mean a ballast resistor. Often a faulty resistor (or one wired incorrectly) would burn up the points quicky. I guess it's possible that the condensor could be affected......I'm not sure we have enough information to make a reasonable guess.

Anyway, if you wish to check your ballast resistor wiring, you can refer to the diagram below for a guide. Your race car likely has a seperate Ignition toggle switch and Starter button (and maybe a fuel pump toggle swith) but it's basically the same as you see below. On British cars, the solenoid is not attached to the starter, but again, it still works the same.

My race-Spridget actually runs current throught the ballast resisitor all the time and it starts fine. In other words, I do not have the bypass circuit (blue wire) that attaches from "i" on the solenoid to the coil side of the ballast resistor.


When you get a chance, ~Click Here~ (https://www.britishcarforum.com/bcforum/ubbthreads.php/forums/32/1/New_Member_Introductions) and introduce yourself to the entire BCF group. :thumbsup:

Michael Oritt
12-06-2008, 10:53 PM
Both of my street Healeys have Mallory Unilite (solid state) systems and as the instructions strongly suggested I installed ballast resistors (wired in similar to Nial's diagram) to reduce the operating voltage and so extend the life of the module which is apparently easily damaged by full (12+)voltage.

What is the reasoning behind installing a ballast resistor in a points system as the diagram shows? I did not realize that points could be damaged by high voltage--is it perhaps to protect the condenser?

BTW Nial, where did you get that nifty diagram?

12-06-2008, 11:19 PM
The ballast resistor is to protect the coil. Low primary voltage coils with good windings are capable of high secondary (spark) voltages for running. Started motors drain batteries, so the resistor is bypassed so the coil gets full battery voltage, but only while starting.

12-07-2008, 12:12 AM
I have never heard of using a ballast resister on a race car???

Everybody I know runs dual points or Pertronics...

12-07-2008, 07:28 AM
Michael: I got the diagram from:


I figure old trucks and British sports cars are similar technology :laugh:

I have never heard of using a ballast resister on a race car???
Everybody I know runs dual points or Pertronics...


As Roger says, the ballast resistor is designed mostly to protect the coil. But excess curent will also cause the points to burn up somewhat sooner (not such a big deal in a race car). Personally, I also think the ballast resistor acts as a electrical "cushion" for the Pertronix unit (that's why I run it all the time....even when starting).

Some coils are "internally ballasted" (most Lucas points-type coils, for example), and do not require an external ballast resistor. Pertronix also sells a special "matched" coil that does not require a ballast resisitor. As far as I can tell, it is also "internally ballasted" like the Lucas coils.

But Pertronix also provides instructions for wiring <span style="text-decoration: underline">with</span> a ballast resistor (if you do not use their "matched" coil).
You can see those instructions ~HERE~ (https://www.pertronix.com/support/manuals/pdf/ignitor12vneg.pdf)

I have never been 100% sure how an "internally ballasted" coil works, but I *think* it just has enough internal resistance so that it acts like its running a ballast resistor all the time (like my setup above).

By the way, I am running a $12 "Chevy" points-type coil and $4 ballast resistor (both made by "Standard") bought at my local discount auto parts store. Technically, these coils are sometimes called "6 volt coils" (even though they are used in a 12 volt sytem) because they run on approximately 6 volts when fed by the ballast resistor.
Combined with the Pertronix, my cheap setup makes a scary-big spark and has been reliable for the last four years.

12-07-2008, 01:22 PM
Thanks Roger
I had it running this afternoon
Many thanks
Glenn (grampy)

12-07-2008, 01:24 PM
Thanks for your help
Had it running this afternoon
Glenn (Grampy)

Hap Waldrop
12-08-2008, 08:19 AM
Hello Glenn, I'm up in Greenville, I've been racing Spridgets and MGBs for 25 years, and now build engines and carbs for race and street performance, if I can ever be of any help, give me a hollar.

12-08-2008, 05:36 PM
Thanks Hap
I got the midget running and took a run through the neighborhood, woke up some retirees. I look forward to seeing you at 2009 events. I'll head up your way when I get the chance. Will you be at Hutchenson Island or the Mitty

Hap Waldrop
12-12-2008, 07:45 AM
I'm always at the Mitty useally vending for Superlite Wheels in the infield. If you run HSR events, you probably know Red Bordner ( Blue NAPA Midget), I build his engines. Everybody knows Red, because he cook BBQ for everybody at the Mitty.