testing a starter switch

1930artdeco

1930artdeco

Well-known member
Ok, I have an issue with my Y block running-or not running. for some reason the car will fire off and immediately die. It was recommended to jumper the ballast resistor and see if it still ran. I jumpered it and it ran for a few seconds so I shut it down-which is good as the jumper wire was hot. Great, I ordered a replacement resistor and swapped it out. Tried last night and she did the same thing fire/die.

So what is the best way to test my starter switch? I will test the new ballast resistor to see what I get for numbers. This is holding me up from doing other tests on her.

Thanks,

Mike
 
I would start by placing a volt meter on the positive connection of the coil. If you have good voltage when the car dies, maybe look for fuel or distributor problems. It does sound like maybe your ignition switch works in start mode but not run mode.
 
When this first started if I kept it in start mode the car would run but the sec. I let the key return to run it would die.

Mike
 
This diagram was drawn for 55/57 T-birds but the only difference should be the right front inner fender location of the starter solenoid. (it's up on the firewall behind cyl 8 in '55/'57 Birds)

With the key switch in the 'Run' position there should be 12 volts on the Red/green wire connection of the ballast resistor.
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  • 12v Ignition wiring diagram, ballast resistor.jpg
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I only got 11v at across the resistor. and infinity ohms. I will have to check the new one and run some tests.
 
1930artdeco said:
I only got 11v at across the resistor. and infinity ohms. I will have to check the new one and run some tests.
Click to expand...
With the key switch in the Off position and connecting a volt meter to the two main battery terminals what voltage are you getting? Should be at least 12v, almost 13v.

Setting the meter to read Ohms, temporarily disconnect the other wires on the ballast resistor and put a meter lead on each of the two ballast resistor terminals. If you're getting infinite Ohms the ballast resistor is 'open', it has no internal connection and will not provide power to the ignition coil. Replace the resistor.
 
When the key turns to “start” all the other power (accessories and run position) goes off. The only power out goes to the solenoid. When it closes, power goes to the starter motor, and (from the second small terminal on the solenoid) directly to the coil. This allows a full 12 volts to be available to start the engine. When you release the key it returns to the run position, and there’s power to the coil thru the ballast resistor. The gauges, etc. come one. And all the accessories like the radio, heater etc.

If it start initially and dies on release it’s either a bad ballast resistor, a bad wire to it, or a bad switch. I suppose a weak coil might fire at a full 12 volts and not at 6-8 thru the resistor, but I haven’t seen that.

I’ve had numerous friends wire in electronic ignitions and the engines spins and doesn’t fire. Let go of the key and varoom it lights off. That’s how I learned about those bypasses. Not just Fords.
 
The ignition/starter switches control multiple separate circuits. The start circuit to the solenoid and the ignition circuit to the coil, BUT, as was mentioned, there can be a ballast bypass circuit to allow 12-volts to the coil only during the start phase and then back to reduced voltage after the start function is released to run position. The start relay usually controls the bypass function. There is a circuit for the instruments as well. The ignition switch also provides power to the generator light if so equipped. The voltage regulator cut out pole is what opens that circuit after the generator comes on line. These other parts of the switch could have an effect on the ignition circuit if there is an open or short anywhere in the run circuits of the switch.

Bypassing the switch to the coil should be run through the ballast resistor to drop the run voltage to the coil. A 1.5-Ohm coil will work on 12-volts but the current is too high for anything but momentary operation. All components and wiring can be checked with an Ohms meter but the circuits have to be isolated for each wire. Checking voltage on a circuit with a resistor can be in question to the average mechanic. Voltage has to be checked across the resistor to catch the voltage drop otherwise it will always give system voltage if checked at the coil. Ballast resistors are generally around 1 to 1.5 Ohms if checked with an Ohms meter. The wires should give little or no resistance and should have infinity Ohms to ground. This is how you find a wire shorted to ground.

Another thing to consider is if the vehicle has an overdrive transmission. The Borg Warner electric OD transmissions have a kill circuit that is controlled by the kick down switch and the operating solenoid. It cuts power to the coil momentarily during kick down to insure the drop out of the overdrive solenoid. If there are shorts or component problems with this circuit, it may have a detrimental affect on the ignition coil function.
 
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