seed sensor help...model 77 air champ

Got the planter out today to check it over and want to try and get the monitor working for this year.  Planter does a good job, but the indicator lights weren't working on the monitor at all last year.  I did wiggle the connector with the 10pins in it, and I got a few blips of light out of it.  But I'm wondering how is the sensors supposed to check out?  They have 3 wires going to each one, a red, green, and black.  What kind of resistance should I get through the sensor?  or should I?  or how does the system work?  (What wire does what?)  The wires have some corrosion, so I'm going to check them out and see what that does.   In the meantime, thanks for any help.  -Wes

Hey John..!  We're using an AC branded monitor that looks Identical to the Dickey-john monitor on the older plate planter we have.  Exact make/model, I'm not sure without looking..I'll check on that tomorrow for ya.  But it helps knowing what wire is what now.  Me and Dad were looking busy checking resistance through the wires..lol  We were having trouble getting the meter to show a good circuit on the black wire at the plug--not sure which of the three wires we were on at the sensor connector though.  As for checking the sensors..I see that Shoup has a tool for that, but, if I leave the green and black wires hooked up, and set my meter on the red wire, and drop seeds through the sensor, won't I be able to see a reading on the meter from the red wire?   Thanks for your help!   -Wes

I might have some NOS sensors      bgtbran@hotmail.com