help with tach hook up

[dubie]

I robbed this tach out of a 72 tow truck a couple years ago at the local auto ranch. My question is, which wires go where? I know one of them will go to the HEI but not sure which one. I have included 3 pics, can anyone help me out?

[67cst]

tim- i wish i knew forsure, ive only done a tach once, and it had 4 wires, they were power, ground, post on coil, and.....maybe acc....i know this doesnt help at all but it will give you a ttt

[dubie]

Thanks man, I am at the shop and should be ready to fire up the beast for the first time and would like to hook up a tach for the start up.

[Bowtie67]

Dube, Process of elimination without the manual, The 2 outside wires (appearing to be pink) that are going into sockets are your bulbs these go into the parklights/dashlight circut. The one wire being held on there by the nut looks to be a ground, if you pull the nut off and it looks to be identicle to the other one with no insulator then it's a ground and should be replaced by a black wire. Now that leaves the group of three, Black is 99.9 times ground that leaves the real 2 important wires blue and what looks like to be yellow or white, I would almost bet the blue is for the tach signal going to the coil and the other is for ignition. Hope this helps, also note that the group of three wires is the same as the three in a row studs next to where the wires come out.