My block heater quick working on my 01 Cummins. What can I do to test or just diagnose the problem?

 

Using an ohmmeter, check for continuity between the 2 prongs on the plug. There should be approx. 19 ohms resistance. While measuring, wiggle the cord right at the plug and monitor for change. That's where most wire breakage occurs. If you see no continuity, remove the cord from the block heater, and test between the pins at the block heater. Also check for signs of heat and melting right at the block heater pins.

 

For figuring out.

W = Watts
V = Volts
A = Amps
R = Resistance

W = V x A V = A x R
This is for basic electricity only.
You can take the meter leeds and put them on one end of the plug and find the other end female end the wide opening is the neutral and the male end has silver for neutral. If one end is bad cut it off and get another end and put it on for a ex cord.

 

If you get an open circut reading , check right at the plug end , I've found far more broken wires at this spot than bad heaters , the plug flops around and breaking the wires inside the insulation so it still hangs there but no conection.