MTFCA Forum

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?

"IN3491" is the part number for a diode... https://www.ebay.com/itm/144864349172?h ... R_aQ2rPNYg

A volt/ohmmeter test can determine whether it's meant for positive or negative ground.

A simple test is to put the cutout on a generator with the generator terminal connected.

The generator does not have to be on an engine for this test.

Connect a 6 volt battery negative terminal to the generator case.

Connect the other cable to the battery positive terminal and touch the other end to the cutout wire to battery position and if you get a spark the diode is conducting.

Reverse the battery cables and touch the negative cable to the cutout battery position and if you do not get a spark the diode is not conducting.

So, the cutout is for a Model T.

There is always a possibility that either test will provide a spark, if the diode is shorted and no good.

Short of opening it up and examining the diode connections, it can be tested to see which polarity it is designed for.
Aside from an ohmmeter test, a circuit can be built with a test light and battery: If it lights up as shown it's negative ground. If it lights up with the battery polarity reversed, it's positive ground. If it lights up both ways or not at all, it's faulty. Of course, this is applicable to diode cutouts only. Mechanical cutouts are not polarity conscious.

FWIW that is an A model cutout. TheT model ones with which I am familar, have both contacts on the flat. Being A model specific, should it be positive earth?

Allan from down under.

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