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Testing a ballast resistor


greg g

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Having an intermittent engine shutoff in my 56 off topic pickup. Stalled when encountering a bump, wiggling some wires showed arching at the coil end of the ballast resistor, so I replaced it, now in the garage the engine starts, runs for 13 seconds then the electrical system shuts down.  After scratching my head and checking new battery and connections checking connections at ign switch everything seems proper.  Tested the old resistor with battery power and meter. It shows 12 volts at both ends regardless of which end is connected to the meter.  probing the resistance coils shows 12 volts along it's length. I will pull the new one and check it in the AM I also tested one of those old style rotary resistance heater switches and it also shows 12 in 12 out at any position of the resistance knob.  Is there something else I should be looking for.

 

It also seems that the whole system is shutting down as after it quits the whole system is down as the solenoid won't respond so maybe my old universal ign switch is toast and the problem not the resistor. I will see what happens by putting the 9ld sparky resistor back in after checking the switches functions.  This am it started right up backed out of the garage and idled no problem for 10 to 15 minutes.  Arrgghh!

 

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Measure the resistance (ohm) of the 'ballast resistor' not voltage.

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  I had a problem kind of like that, changed condenser. Happened again, added ground wires, happened again. I cleaned the wires to the back of the AMP gauge. So far so good. You could just put a jump wire between the terminals on the gauge and see if it runs longer. Could be a be an oxidized connection at the gauge. 

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6 hours ago, greg g said:

Once more in electricity for dummies language....

 

When there is an open circuit (not a completed circuit to ground) there won’t be any current flow. Without current flow the resistor won’t drop the voltage. Hence you have the same voltage readings at both ends. When you add another load (ie. the coil) to the circuit and current flows you will be able to measure the voltage drops across both loads. Or you would need to measure the resistance value, in Ohms, and calculate the voltage drop(s) using Ohms Law. Voltage = Amperage X Resistance (V = I x R)

Edited by Merle Coggins
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I'm really impressed. Never knew Chrysler started using ballast resistors and coils in 1956. Or is it newer aftermarket?

 

Merle Coggins is correct. Measuring resistor voltage drop should be done with closed points so current can flow to ground. If you have 12 volts on both sides of resistor, then look elsewhere for fault. Ballast resistors Ohm value is so low most instruments can't measure them.

Edited by chrysler1941
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1 hour ago, chrysler1941 said:

I'm really impressed. Never knew Chrysler started using ballast resistors and coils in 1956. Or is it newer aftermarket?

 

Merle Coggins is correct. Measuring resistor voltage drop should be done with closed points so current can flow to ground. If you have 12 volts on both sides of resistor, then look elsewhere for fault. Ballast resistors Ohm value is so low most instruments can't measure them.

The vehicle in question is a 56 Studebaker with a 64 Studebaker engine.  The coil was on further investigation leaking oil so I replaced that with a new one, installed the new resistor started up, quit 3 minutes later.  So in the meantime I decided to power the input of the resistor with a jumper wire from the battery side of the solenoid.  Hey Presto starts and runs till I take release the alligator clip. Guess there is a change of ignition switch in my future.  At least I can now get it to a cruise in tonight and the Studebaker Zone gathering tomorrow.  I am giving some thought to wiring the coil through what used to be the dashboard toggle for the no longer used electric fuel pump.  And changing the switch at my liesure when the heat abates.  See trouble shooting still works...   

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Ok!  New coil, new battery, new baast resistor, new ign switch (the cause of the original fault) alternator tested good including diods. All fixed!  No, Now alt light comes on and stays on when ign is off and key is out.  GM internally regulated with wiring the same as pre fault conditions.  Been removing batt cable when shut off.  I thought the idiot light was supposed to stop back feeding on shut down.  Charge rates 13 to14 volts less than 10 at idle.   Arghhhh!

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12 hours ago, greg g said:

Ok!  New coil, new battery, new baast resistor, new ign switch (the cause of the original fault) alternator tested good including diods. All fixed!  No, Now alt light comes on and stays on when ign is off and key is out.  GM internally regulated with wiring the same as pre fault conditions.  Been removing batt cable when shut off.  I thought the idiot light was supposed to stop back feeding on shut down.  Charge rates 13 to14 volts less than 10 at idle.   Arghhhh!

What kind of alternator? GM or the small popular Denso 60A ? 1 wire or 3 wire ?

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you need to add a diode as per attached pic

This one shown has the diode under the shrink tubing.

Diode pointing toward the alternator. This prevent alternator back feeding powerback to ignition switch -keeps motor running!

 

 

 

DJ

Screenshot (1).png

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