I'm really ignorant about diodes. I found 1 on my John deere tractor. It has no continuity in either direction. I believe it's bad. How do I identify it so that i can purchase an equivalent? thanx.

 

You could start by posting a picture of it, and even if you can't do that right away, a description would help: what does it look like, how big is it?

Mention of any codes marked on it would be a start. You might even find that you could find out about the device by putting them in a web search.

Of course, you would do well to make sure that this is a diode - what was it doing on the tractor?

 

It's about 1/8" long cylindrical like a resistor with silver band over 43 over 004. It was encased in silicone which I split/cut and in process may have scratched off markings. I'm trying to learn what it does; haven't yet followed the wiring; was hoping someone had been here before and would know about john deere which tries to keep their wiring diagrams secret. JD calls it a diode in their parts listing. I want to understand what I'm doing rather than just replace a part. Thanx again

 

Could it be 1N4004? Often the 2nd line is "004"
Very, very common diode--used everywhere
General purpose

 

Is the diode in a voltage regulator asssembly? If so, it might be a Zener, like a 1N5343
http://www.onsemi.com/pub_link/Collateral/1N5333B-D.PDF
The more information you give us, the better our "batting average" will get.