1972 GMC tachometer problem

[tmarvin]

Hey guys this is my first attempt at this forum so please bare with me. I have a 1972 GMC 4x4 and recently purchased a stock tach from LMC. I removed the old bezel ( Instrument panel) and installed the tach. On the rear of the tach are three electrical connections. The middle one is a nut and is obviously the ground. The other two one goes to the distributer and the other to a power source. I do not know which one goes where. I contacted LMC and the tach did not come with instructions. My concern is if I hook it up wrong I could damage the " expensive" tach. Can anyone help me a pic of the rear of the tach would help tks in advance