Resistor update

I am still having trouble with the resistor getting so hot you can't touch it on this ford 240 engine it will crank and run good and go to the resistor and it has volts coming to it but none coming out of it to coil or distributor let it cool off and it will run put it in gear and it dies and no volts at the coil coming out of resistor
. I need some help thanks

I would guess the coil is partly shorted, drawing too much current overheating the resistor. Do you have another tractor you can borrow the coil from?

No but I will be at Napa in the morning and get one they aren't that expensive

What have you done so far?

If you haven't replaced the coil, try removing the wire from the distributor side of the coil.

If the resistor keeps heating, the coil is shorted internally.

Does it have the resistor bypass wire from the starter solenoid? If so, is that wire possibly shorted to ground? Try removing it from the coil/resistor.

Hi

May not be your problem, but I have seen where when the resistor heats up the wire expands and touches metal behind it which shorts out part of the resistor. This kills power to the load and causes the remaining part of the resistor to get even hotter.

Try measuring the current when points are closed. It should be around 4 amps or slightly less. To reduce current large resistance.

When the points are closed on my Jubilee the current is 4 Amps, and I measure 6v drop across coil and 6v across resistor.

Get a resistor for a 1966 Chevrolet 6 cylinder Biscayne. They are cheap and work. us a resistor needed coil. Jim

If the downhill output side of the resistor has voltage on its input, but none ever on its output, there must be a short from ballast output to ground causing it to draw excess current constantly and yes overheat OR THE BALLAST IS AN OPEN CIRCUIT. On the ballast output, which is the coils input (NOT to distributor side), with ignition on and points closed Id expect around 6 volts there UNLESS there's a short to ground. Then over on the coils other output to distributor Id expect 12 volts when points are open, but zero ONLY when they are closed.

Look for a short in the circuit from ballast output which should normally be to and through the coil to the opening and closing points (in which condenser is a parallel path) then to ground ONLY if points are closed. If the coils LV primary is only shorting once warmed up that could allow it to run a while then die.

If the condenser is shorting out (could happen only after its hot ???) that would cause constant coil and ballast current (no opening of points to break the circuit) which will overheat and there wouldn't be any spark.

I would check ballast resistance when cold and warm,,,,,,,,,,insure points are opening and closing,,,,,,,,,,,check coils LV primary (+ to - terminals) it should be around 1.2 to 2+ ohms,,,,,,,,,,,,,,,,check condenser it may be shorted or shorting once hot,,,,,,,,,,insure the distributors pass thru stud insulator (where wire from coil attaches) isn't shorted to case.

Since the condenser can act up when hot and its much cheaper then a coil, try it first. However the coil may short only after its hot also. Coil and condenser are a couple prime suspects and sure the ballast resistor could have a problem so check that also, but there can be other problems, post back if it isn't condenser or coil and we will take it from there.

It obviously cant fire if there no volts getting to the coils input and cant fire either if the coil or condenser is shorting when hot, neither can it fire if the ballast became an open circuit (high resistance) but once it opened fully it should stop drawing current and cool off.

The coil and condensor and ballast aren't hard to troubleshoot, if its not the points or a wire shorting one of those three may be the problem

John T

I have been reading some of the archives and I wonder about that wire coming fron
m the I side of the solenoid,I just replaced the solonoid the other day and this problem has come up and I am wondering if maybe it is still feeding it 12 volts and not cutting off once the switch comes off of start. I am going to try disconnecting that wire at solenoid and see what happens the solenoid may be the problem,what do yall think?

The solenoid to coil wire If disconnected at the solenoid should be at reduced voltage (maybe 8 volts while running) and the terminal on the solenoid should be dead (no volts) if voltage there, it would heat the coil, not the resistor. The only ground should be the points. Jim

Instead of the bypass terminal feeding power all the time, which would result in the coil overheating, and burning the points prematurely, it would also cause the engine to continue to run with the ignition off (provided the coil wasn't so hot it was failing).

I would look for the wire being pinched, touching ground intermittently, or a problem inside the solenoid shorting the terminal to ground.

Try disconnecting the bypass wire at the coil, tape it so it can't short to ground. It will start and run without the bypass connected.

(quoted from post at 21:11:44 09/23/19) Get a resistor for a 1966 Chevrolet 6 cylinder Biscayne. They are cheap and work. us a resistor needed coil. Jim

Click to expand...

ow, that is funny! Biscayne, as opposed to any other model of 6 cyl Chevy? :lol:

Sounds like a bad coil to me.

(quoted from post at 02:11:44 09/24/19) Get a resistor for a 1966 Chevrolet 6 cylinder Biscayne. They are cheap and work. us a resistor needed coil. Jim

Click to expand...

I've never seen a resistor on a 66 Chevy. My Caprice had a steel resistance wire going to the hot side of the coil.

If your bypass is attached to the start side of the solenoid, the ignition voltage will see the input side of the resistor, the output side will see the coil, and the starter motor as a load. The starter motor has near zero resistance, and looks like a direct ground. That would make the resistor glow.
If the bypass wire is fitted with a diode the diode will prevent back flow to the starter. (positive ground, band end of diode toward coil, if negative ground, band end goes toward starter. 4 amp diode is needed with 250 piv) Jim