[SAAC2110]

Hoping some of you gurus out there can let me know how to test a pontiac in dash tach by itsself ? I picked up one for my 68 GTO and later got another one with a rally dash package I couldn't pass up. The following summer I got a hood in pretty good shape but it already has the hole cut-out for the factory hood tach and would rather just go the hood tach route on the GTO and keep the clock in the dash. I plan on selling them to help in the purchase of a hood tach but would like to know if they are both functional - I was told they were from the purchasers but everyone knows how that goes.... Each tach has three small studs and one insulated stud with a nut on it, one has a push on contact for a wiring connector on the stud. I think they are for different applications since one has the bottom mounting hole off to the side and the other is straight up and down. Will try and get pictures posted of them but for right now just want to know if they work or are just for parts.