Red one with bulb? Well light! The other red one...is it insulated from the tach with a grommet? If so its not a ground. Without seeing inside the tach, the other three could be anyones guess, but you do have these to make it work. 1-Ign ONLY, hot when key is on. 2-Dist.connection, neg.side... 3-Ground. 4-Light. 5-? Know this is not the best help you can get, does that tach have a name on it? Looks to have been thru some rough times.