Polarity help
 

Finally getting around to replacing the Krap in dash tach I had. You can see them side by side below. Old one was plastic and pretty hollow inside.

Anyway my question is around bulbs. The old tach bulbs used I rubber socket end and there was a separate ground wire on back. Those rubber sockets in the pic below do not fit in the new tach holes. So I guess I am going to cut them out of wire and replace with a standard socket. Notice there are two wires per bulb. Can I splice those together and then tie in a regular socket for an 1895 bulb? I think so, but wanted to confirm.

Bulb type also pic below.

Current bulb in rubber socket

Your old sockets had 2 wires? Then 1 is a ground wire and 1 is a power wire. If you connect them together you will have a dead SHORT to ground. The bulb you show in the picture takes a socket with separate power and ground wires like your old ones. If the old socket is slightly too large enlarge the holes in the housing. If the old socket is too small you will have to find 2 wire sockets to fit the housing.

I may have misread your post. If you want to use a bulb with 1 contact you need a metal socket with 1 central contact or a plastic socket with a central power contact and a second wire that contacts the side of the bulb. If you use a metal socket just use your present POWER wire and make sure the tach housing is grounded to the car either through the dash or a separate wire to the body. You won't need the ground wires unless you want to use them to ground the housing. If you get a plastic socket with a central power wire and the side ground wire just connect it the same as your present sockets.

Ok got it. Thank you for clarifying. I’ll just figure out which one of the two wires is power and use that with a new spliced in metal socket. There is another ground wire on the tach body so I think I should be good.