Ghost In the Machine

[Mark Jones]

The weekend before last, I installed a new gas tank/sender/filter and my rebuilt differential. At that time, I took my 72 (Lucy) for a quick ride around the block just to make sure everything was working, and I didn't have any unwanted noises. She went into the garage until this weekend. I had planned on a weekend cruise up the Cali coast and when I went to start her up - No Fire? Not even a sputter. The battery was up to charge and I had fuel. What could be wrong. I checked for the accelerator pump shot and that was good. I checked cap/rotor and plug wires, they all were seated and secure. I pulled out the volt meter to check for ignition voltage at the ballast resistor and found 7 volts DC going in (IGN switch side) and 4 volts DC going out to the coil. The voltage readings seemed too low so I clipped a jumper for the battery terminal to the IGN side of the ballast resistor. The engine fired right up. I pulled off the jumper and the engine died. I re-connected the jumper and started the engine again and let run until it was off its choke cycle. When I pulled the jumper this time, the engine stumbled slightly but kept running. I have a new ignition switch (China) so I am assuming that my old ignition wiring from the ignition switch to the ballast resistor will need to be replaced. Could 50 year old wiring develop such a resistance to drop 12 volts to 7 volts. There are a couple connectors in the path and I guess it's possible that the terminals are a bit oxidized and maybe causing some resistance or a poor connection.
Needless to say, I didnt take my drive and it may be till after Christmas and New year's before I dig deeply into this. Any thoughts or comments will be appreciated.

 

[Don C]

Unfortunately, new does not mean good.

The ignition circuit has a built-in resistor. The portion of the wire that runs from the ignition switch to the coil (red with light green stripe) that is under the dash is a resistor wire that should measure around 1.4 ohms. It will reduce the voltage to the coil to around 6 volts. When you crank the engine full battery voltage should be delivered to the coil via the "I" terminal on the starter solenoid.

You say you checked the voltage at the ballast resistor. Does your car have a ballast resistor in addition to the resistor wire? With the voltage you say you have going into the ballast resistor, and then out of the resistor to the coil, I suspect you do.

 

[Mark Jones]

Thanks for the reply Don. That is a very good comment and got me thinking. After looking at the 1972 schematic book I have, I suspected the same thing. The low voltage from the ignition key seems that it would be correct if I have the resistor built-in to the wire. i guess i could extend the leads on my meter and check the resistance of the ignition wire to see how much resistance it has. In addition, I believe that I do not have the coil "I" connection to the starter solenoid which could be the second issue for the "No Start" condition.
I dont have any history with the car and the ignition was modified before I became the owner (addition of Mallory 604? points replacement device). The ballast resistor is the OEM Ford resistor so I assumed it was OE stock and the Mallory instructions does say to use the ballast resistor. Maybe I should just take a chance and jumper the resistor. The worst that could happen is burning out the coil. I need to search out the starter relay "I" connection which should be easier than getting under the dash and messing with the ignition switch and related wiring. Thanks again

 

[midlife]

Yup, not having the I from the starter solenoid not connected will cause the engine not to start. Fix that!

 

[Mark Jones]

I had to move the car out of the garage last night to access Christmas decorations. The engine did start and my curiosity was rampant. While the engine was running (cold and stumbly high idle around1000rpm) I connected a jumper wire across the ballast resistor. There was a slight spark and the engine rpm went up 300 rpm and the engine running smoothed out quite a bit. I blipped the throttle to release the high idle cam (I expected the engine to stumble and then shut off) and the engine settled down to 850rpm (dash tach reading) and idled smoothly (engine still stone cold). I am strongly thinking that my ballast resistor does not need to be in the circuit.
I have not checked the "I" connection to the starter solenoid, but I do have the OE slip on plug connected to it. I have to do a continuity check and see if the wire is connected to the coil. I suspect it might be connected as it should.