Gasoline

Hello!

It is an unusually hot summer and last week my Mustang 1971 was shaking and finally died and was impossible to start even though I tried with a new ignition coil. I manage to start it later after putting in a new condenser, but the next day the problem happened again. This happened when the engine was hot and I think it's the external ballast resistor causing it because I suspect that I already have a resistance wire.

I have Mallory distributor with dual points, MSD Blaster 2 and according to the manual I have to use a ballast resistor, but shouldnt this be a problem if I already have a resistance wire? I guess the combination causes the car to die when the engine is hot (it gets too little spark). How do I measure so I know for sure that I have a resistance wire? I guess some previous owner did not use a distributor with points.

dawson1112

I wonder if you could get me a couple pics of how the ballast resistor is wired up.
The coil calls for an external ballast resistor . If your using both then I would think that your lowering your voltage to the coil below what it should be.
Now when the coil gets hot it adds resistance causing a failure. You will end up likely burning through coils.

dawson1112

if your using a resistor wire you don't need the external resistor.
How ever the external ballast resistor is much better at maintaining the correct voltage through out temp changes.
There should be a wire that goes to the starter solenoid by passing the resistor during cranking for easier starts.
Once the car is running the coil gets its power through the resistor wire or ballast resistor. while the engine is running you should see a minimum of about 9-10 volts. If your not getting that your coil is not going to have the voltage to maintain spark. Tell tail signs of a resistor wire is a thick looking pink wire that comes from the ignition switch. I cant remember for sure what color the wire going to the assy on the solenoid is but I think its green or blue. This wire will come back to the coil and by pass the resistor.

Gasoline

I contacted Mallory and the distributor needs 3 ohm (resistance wire 1.5, coil 0.7 and ballast resistor 0.8= total 3 ohm) so I seem to have the right parts installed.

However, doesnt this extrem warm summer increases the resistance?

dawson1112

Im not sure how yours is wired up , I know that on some of the earlier models the ballast resistor has a low value in resistance when cold to allow for an easier start. And as the temp rises it gradually increases resistance.
It is possible that your resistor is shot and the resistance is way to high once it gets hot.
One way to tell is to check your voltage at the coil when the engine is cold. Allow the engine to warm up take a drive what ever till it starts to give you trouble then measure the voltage to the coil again.
If your coil is close to the engine possibly relocate to a cooler area. Most of the time the coil is mounted on the front of the engine and can get quite hot. Yes heat will increase resistance.

assuming your engine is mostly original and has a carb, check the fuel lines to see if they are getting hot any where. Back in the 70s it was not uncommon to see cars sitting on the side of the road in extremely hot weather due to vapor lock.

Gasoline

The ballast resistor goes up to 1.5 ohms when hot.

I´m guessing I could skip the ballast resistor by buying a ignition coil with 1.4 primary resistance and combine this with the original wire resistance in the Mustang which is 1.5?

Thomas

dawson1112

How did you know my name lol haha my name is Thomas as well.

dawson1112

It sounds to me like the ballast resistor is doing its job when it gets hot. If you get rid of the resistor wire you would probly be in the ball park of where you need to be

By the way that's a beautiful car man.

dawson1112

You could aways go with a coil that required no external resistor. My 68 302 points engine used one like that. It was a simple 12 volt wire from ignition and a duel points dizzy . The coil said on the side of it do not use external resistor.

Starfury

The Blaster 2 is designed for use without an external resistor. It's the points that are the problem. If you feed 12V to points, you'll burn them up in no time.