The Ford Barn

29spcoupe · 09-06-2023, 11:00 AM

I have found in my stash of parts what is either a cutout or voltage regulator or possibly a diode cutout. Is it positive or negative ground. The reason I am asking is do I keep it for my Model A Ford or sell it because I no longer own T's?

Gary WA · 09-06-2023, 02:57 PM

does it look like it was taken apart to install diode?

Bob C · 09-06-2023, 03:55 PM

1N3491 is the diode.

Bruce of MN · 09-06-2023, 04:37 PM

You should be able to use voltmeter on the output terminal and case, with test leads from your battery to see what polarity it is.

nkaminar · 09-06-2023, 05:04 PM

The diode case is negative in the forward direction. So if wired for a positive grounded battery, the terminal on top of the diode would go to the pole on the generator and the case would go to the battery. The diode is low leakage.

As Bruce said, you can use your multimeter to test how it is hooked up. Set up the meter in the ohm measuring mode. Put the positive (red) lead on the the terminal that would normally go to the generator and the negative (black) lead on the terminal that would go to the battery. You would measure low resistance if it is for a positive grounded battery. Now reverse the leads and you should find high resistance. If the reverse is true then it is for a negative grounded battery.

Data sheet is here: https://datasheetspdf.com/pdf-file/1...orola/1N3491/1

29spcoupe · 09-06-2023, 08:48 PM

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Thanks, it looks like I have a positive ground unit for a Model A.

09-06-2023, 02:57 PM	#2
Gary WA Senior Member Join Date: May 2010 Location: Clinton,WA/Whidbey Island Posts: 4,140	Re: Cutout confusion does it look like it was taken apart to install diode? __________________ www.whidbeymodelaclub.com

09-06-2023, 04:37 PM	#4
Bruce of MN Senior Member Join Date: May 2010 Location: VA Posts: 1,434	Re: Cutout confusion You should be able to use voltmeter on the output terminal and case, with test leads from your battery to see what polarity it is.

09-06-2023, 05:04 PM	#5
nkaminar Senior Member Join Date: Jan 2012 Location: Western North Carolina Posts: 4,002	Re: Cutout confusion The diode case is negative in the forward direction. So if wired for a positive grounded battery, the terminal on top of the diode would go to the pole on the generator and the case would go to the battery. The diode is low leakage. As Bruce said, you can use your multimeter to test how it is hooked up. Set up the meter in the ohm measuring mode. Put the positive (red) lead on the the terminal that would normally go to the generator and the negative (black) lead on the terminal that would go to the battery. You would measure low resistance if it is for a positive grounded battery. Now reverse the leads and you should find high resistance. If the reverse is true then it is for a negative grounded battery. Data sheet is here: https://datasheetspdf.com/pdf-file/1...orola/1N3491/1 __________________ A is for apple, green as the sky. Step on the gas, for tomorrow I die. Forget the brakes, they really don't work. The clutch always sticks, and starts with a jerk. My car grows red hair, and flies through the air. Driving's a blast, a blast from the past. Last edited by nkaminar; 09-06-2023 at 05:11 PM.

09-06-2023, 08:48 PM	#6
29spcoupe Senior Member Join Date: Aug 2014 Location: Rhinebeck, NY Posts: 763	Re: Cutout confusion Sponsored Links (Register now to hide all advertisements) Thanks, it looks like I have a positive ground unit for a Model A.