Thanks Ed I used to cary a flash light set up to do that but I got a handyman and gave it to a new tech some years back.Saved my tail many times and cheap to set up.

The important thing here is, when replacing either SCR2 of 5, I also reccomend changing the filters. These can check out ok but can give strange faults. Indeed many SCR2 & 5's have been changed when in fact only the filters needed to be replaced.

Use a handyman from flight systems and load it up see if it swaps will show good or bad.There is also a way to wire a flash light to feild test but off the bat i forget how.

There seems to be a consensus (of two anyway) that #5 gives the most problems. What are you test proceedures for this rectifier?

# 2 is higher capacity than #5 SCR

#5 usually is the problem...there are test procedures which will diagnose all but the tricky ones

You can install a # 2 in either position (2 or 5)

I change them both because the labor is about the same to change one as it is to change both. The parts are about $45.00 each. If I have to make a trip back because I changed the wrong rectifier, I end up doing it at my expense because I didn't get it fixed right the first time. I suppose if I were an onsite tech for a company and they were paying me to be there 8 hours a day anyway, I might change one at a time. Since I have to drive out and change the rectifiers, it does not make sense for me to change just one.
Also, the customer wants me to make one trip and get his truck fixed right the first time. If I don't, he looses faith in me to do my job.
I have not found a reliable test for components in and SCR panel with intermittent problems other than changing the suspected parts and running the truck. I have found components the checked bad with a Handyman or VOM and work just fine. I have found components that checked good be bad. I have sent SCR panels out to be fixed and had them come back with more problems than they had to start with.

Replacing both the 2 and 5 rec used to be common practice. Not long after EV 100 systems came out there was a problem with parts. I worked for Clark then and we were told to replace both as a precaution. I think the part manufacturing problem has been rectified by now. Crown has had a problem with 3 recs made in India. They have changed manufactures. I don't think it is necessary to replace both recs unless they show weakness when tested.

I have alway replaced them one at a time mostly 2 recs dont seem to have much of a problem with the other going out.Wheel cylinders for example I always do as a pair as both are subject to trash in single brake line.Most electrical I only replace whats bad.Id like to see what everyone has to say on this also