Use your DVM. It may have a diode range or else it should read low resistance one direction and high the other. Yours is probably shorted. With Radio Shack gone, I have no idea where you will find one. Rating is not critical. It must fit in the space but the only thing it powers is the starter solenoid.Also there is a band to indicate polarity. New diode must go in the same direction.
Bob

Thanks.
I'll see what's out there... maybe Amazon.

Both Newark Electronics and Allied are good sources for generic electrical odds and ends.
http://www.newark.com/
https://www.alliedelec.com/products/

Thanks!
I also found that Radio Shack has parts available online.

A basic, leaded, discrete diode with the numbers "1004" in them will do everything you need. That's probably the most common one. Your biggest issue is going to be not having to buy 100 or 1000 !! They probably cost 1/2 cent each.

Also, be careful soldering it into place. Heat can kill these units.

Thanks for your help. Not knowing about the "1004" , I ordered about a half dozen different values from Radio Shack.
BUT, while testing with my VOM the Original seems fine: one way was 273k ohms; the other direction was 0L ohms. ???

If your VOM is telling you the truth, that diode is open i.e dead. OL ohms means overload, no current flow, open circuit, DEAD. 273K ohms is the equivalent of an open circuit in a 12 volt system.
The diode part number is actually 1N4001, 1amp, 50 volt. It is the most common diode in existence. 1N4002 is 100 volt, etc. Diodes are hard to measure if they are connected into a circuit. Disconnect the brown wires from one side of the diode to isolate it from the circuit. This diode's function is to prevent the clutch switch from lighting the neutral bulb. If the clutch switch does light the neutral bulb, the diode is shorted.

Again, my thanks.
Being electronically challenged, (my so-called "friends" like to say "if you can run wire to it, Dave can set fire to it") I thought that if the diode gave two different readings, it was doing it's job. I checked my order list from Radio Shack and it included two # in 4001 1 Amp diodes. Beginners luck.
Once they arrive, I have a very small iron I can use to "just melt and get out".
Thanks again for your help.
Dave

I just checked my shipping confirmation from Radio Shack: The diode order won't be here until Saturday 🙁
Oh, well. The transmission is still out being repaired so it would be difficult to find out if my "surgical efforts" are successful, but, again, thank you SO MUCH for your time and expertise! I REALLY appreciate it!
Dave

Again, my thanks. Being electronically challenged...

A common affliction, more prevalent than once believed.

You're simply working in the field known as "Electrickery". 😆