One thing to add, make sure you disconnect the battery cables before messing with the wiring on the back of the alt gauge. The red one is a straight shot to the positive side of the battery, so you don't want to short it out!
Right !
I failed to mention that..... I guess I was hoping that it would be common sense if messing with electrical to disconnect the battery, but if someone never did this before they might not think of that. Thanks for the additional info !