Resistor ignition switch wire

[Mark Jones]

I am looking for a confirmation that my suspicions are correct. I havent made any measurements with a meter yet but that will be my next job when I get some time to devote to this issue. I am working on other areas of the car and I am not driving it at the moment. When the car has sat for a few weeks and the battery voltage is a little lower than full charge, the engine will crank over fine but it wont start. Not even a pop or spit. If I connect a jumper wire from the battery (+) to the ignition switch side of the ballast resistor (white ceramic type), the engine will fire right up. I can let the engine run and charge the battery a bit then pull off the jumper and the engine will continue to run. If I dont wait for the battery to charge and pull the jumper too soon, the engine will die and wont re-start.
I suspect that I may have an ignition feed wire with the resistor built in and I am using the ceramic ballast resistor as well in the ignition feed circuit to the coil. This is the way the wiring was when I purchased the car so I assumed it was correct. It would seem that if I have 2 resistors in the ignition feed line to the coil that I am not getting enough voltage to the coil to get it to fire. The distributor has been upgraded with a Mallory pointless ignition adaptor, and I have a new coil that was supposed to be the OEM 6v type not 12v type. Any thoughts.

 

[Doug's 73 Mach1]

A stock Mustang has a built in resistance wire (behind the dash) feeding the coil, the coil then connected to the distributor. The resistance wire lowers the voltage to the coil and points. This is done to prolong the life of the points. There is another wire at the starter solenoid that bypasses the resistor wire for starting and is only powered while cranking the starter. That 12 volt bypass generates a hotter spark during cranking for easier starts. From your description of the problem, you may have an issue with that bypass wire. There should be no need for another resister in series. Pointless distributors often require the full 12 volts. Mustangs with the factory tach need the resistance wire in series with the coil to function properly. With some pointless distributors, getting the factory tach to work can be tricky.

 

[Mark Jones]

Thanks for the reply Doug. I feel a little stupid as I found out that I asked a similar question just before Christmas last year (Ghost in the machine). The car has been sitting and I tried to fire the motor the other day. I had to use the jumper so I thought I would pose the question to the forum. Between the answers last year and your comments, I know I just need to get into it and get all the voltages right. I am rebuilding the hurst shifter at the moment. When I get that completed then I will get into this ignition thing. I'm likely to replace the distributor and coil with 12 volt electronic units and be done with it all. Thanks again for the advice.