Fender opto isolator "roach" which end is which?

[vortex]

I just got a replacement roach from Kendrick for my silverface DR. I seem to be measuring 2.2M on both ends of the roach! The "suspected dead" roach (in circuit) in the amp measures 47K on one end and 10+M on the other.

I know that if I just pop the new roach in I have a 50% chance of getting it right the first time but is there any other measurement I should perform first to ensure a quick, first try fix?
Thanks!

[Bruce / Mission Amps]

Put your ohm meter on two leads. Set it for very high resistance and shine a very bright flashlight in the open end of the shrink wrap... if the resistance changes dramatically, you have the resistance/photocell end not the neon bulb end.

I woulds guess your +10m is the neon lamp side but this will tell you for sure.