I have found when the 1 rec starts to go bad, the battery voltage get less and less with the truck at rest. 30% of battery voltage is about the threshold that the truck will not run at. 50% or more across the 1 SCR is desirable. Of course, other components in the panel can cause this less than 30%. For the 2 and 5, if I suspect them, I replace them both. Too much labor to do just one, and they are not that expensive. Have not had much luck with the Handyman. They can test bad with the Handyman, and be good. They can test good with the Handyman, and be bad. I just gate them on with a headlight, some jumper wires, and a 12 volt battery. The problem with any bench test is you don't run near the amps through an SCR on the bench as you do when the truck is operating