The Ford Barn

gp1941 · 08-19-2021, 10:40 AM

Gentlemen,
I have 2 (NOS) Coil Resistor Circuit Breaker assemblies for my 41 truck. Both came in boxes labeled 01A-12250. However looking thru the perforated metal cover over the circuit breaker portion there appears to be an obvious difference. One has a few turns of heavy gauge copper wire wrapped around an iron rod. I assume that a "short circuit" overloads the thermal contact and it will "open" the circuit.
The other assembly does not have the coil but has just a thermal contact.
Is there a difference in part number, like a revision, and will both function properly, assuming the parts are not defective?
Thanks for the help.

JSeery · 08-19-2021, 11:53 AM

There would be a letter after the number (01A-12250) to indicate the application. It could be an A, B or C.

rotorwrench · 08-20-2021, 12:56 PM

The early types used the circuit breaker with a holding coil adapted to the breaker. The holding coil allows current to get through even if the bi-metallic switch gets hot. It breaks the circuit enough to keep the lights on but they will likely be dim or intermittent since the voltage is being cut back to keep the breaker temp down which is a lot like the way a constant voltage regulator works as was used in the 50s & 60s to keep the instruments operating at a constant lower voltage. As soon as the short is repaired, the lights go back to normal function.

Later units were just a bi-metallic breaker. The lights are fully intermittent when there is a short on this type or breaker. They go off till the breaker cools then back on till it gets too hot again.

gp1941 · 08-22-2021, 04:36 PM

Thanks,
I checked the boxes today and one does have an -A suffix. The other box has NO letter code. So I have to assume that is the later style.
Any idea what the "cut-out" amp current draw is for the breaker to activate?
I appreciate the input. Always learning something new.

ford38v8 · 08-23-2021, 12:43 AM

Quote:

Originally Posted by gp1941

Thanks,
I checked the boxes today and one does have an -A suffix. The other box has NO letter code. So I have to assume that is the later style.
Any idea what the "cut-out" amp current draw is for the breaker to activate?
I appreciate the input. Always learning something new.

Correction: the lack of a suffix letter would indicate the earliest version of a part having an identical prefix. That said, there may be examples to the contrary.

rotorwrench · 08-23-2021, 11:40 AM

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It may be a later replacement item or it can be one that is made to fit a different application. It just depends since the parts book aren't always real specific. They will generally tell what a different engineering change suffix will fit though. When the part is a replacement, the earlier part number is generally deleted from later revisions of the parts catalog indicating it was obsolete.

My guess is that the holding coil types became problematic with age or they were determined to be more complex than was necessary. If this is the case, the later unit would be the replacement for the earlier type.

08-19-2021, 10:40 AM	#1
gp1941 Junior Member Join Date: Sep 2015 Posts: 25	COIL Resistor-Circuit Breaker Gentlemen, I have 2 (NOS) Coil Resistor Circuit Breaker assemblies for my 41 truck. Both came in boxes labeled 01A-12250. However looking thru the perforated metal cover over the circuit breaker portion there appears to be an obvious difference. One has a few turns of heavy gauge copper wire wrapped around an iron rod. I assume that a "short circuit" overloads the thermal contact and it will "open" the circuit. The other assembly does not have the coil but has just a thermal contact. Is there a difference in part number, like a revision, and will both function properly, assuming the parts are not defective? Thanks for the help.

08-19-2021, 11:53 AM	#2
JSeery Member Emeritus Join Date: Nov 2012 Location: Wichita KS Posts: 16,132	Re: COIL Resistor-Circuit Breaker There would be a letter after the number (01A-12250) to indicate the application. It could be an A, B or C.

08-20-2021, 12:56 PM	#3
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 16,440	Re: COIL Resistor-Circuit Breaker The early types used the circuit breaker with a holding coil adapted to the breaker. The holding coil allows current to get through even if the bi-metallic switch gets hot. It breaks the circuit enough to keep the lights on but they will likely be dim or intermittent since the voltage is being cut back to keep the breaker temp down which is a lot like the way a constant voltage regulator works as was used in the 50s & 60s to keep the instruments operating at a constant lower voltage. As soon as the short is repaired, the lights go back to normal function. Later units were just a bi-metallic breaker. The lights are fully intermittent when there is a short on this type or breaker. They go off till the breaker cools then back on till it gets too hot again.

08-22-2021, 04:36 PM	#4
gp1941 Junior Member Join Date: Sep 2015 Posts: 25	Re: COIL Resistor-Circuit Breaker Thanks, I checked the boxes today and one does have an -A suffix. The other box has NO letter code. So I have to assume that is the later style. Any idea what the "cut-out" amp current draw is for the breaker to activate? I appreciate the input. Always learning something new.

08-23-2021, 11:40 AM	#6
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 16,440	Re: COIL Resistor-Circuit Breaker Sponsored Links (Register now to hide all advertisements) It may be a later replacement item or it can be one that is made to fit a different application. It just depends since the parts book aren't always real specific. They will generally tell what a different engineering change suffix will fit though. When the part is a replacement, the earlier part number is generally deleted from later revisions of the parts catalog indicating it was obsolete. My guess is that the holding coil types became problematic with age or they were determined to be more complex than was necessary. If this is the case, the later unit would be the replacement for the earlier type.