Change 12v switch to illuminated

OK. Here is my solution.

The wiring all has 3/16" spade connectors on 12g wire.

I took a 1" length of 12g wire, stripped both ends, and put a male connector on one end.

I took a 4" long piece of 18g wire and stripped both ends, then put one end in a female connector with the other end of the 12g wire.

I had a light beside the switch to signal a propane burner failure for the water heater. I turned off the propane, turned on the propane heater, and waited for the light to light up. After it did, I determined the polarity and pulled the ground wire off. I put the female connector on the light, and the wire on the male end of the jumper I made.

Then I turned on the electric element (unplugged from shore power) to determine polarity on the electric heater switch.

I then pulled the hot wire from the old switch and put it on the hot terminal of the lighted switch, moved the load wire from the old switch to the lighted switch, and put a female connector on the other end of the 18g wire and put it on the switch's light terminal.

Works like a champ. Now my electric water heater switch lights up if turned on.

Now, I just need to decide if I want to do the same thing for the switches for the scare light and the awning light.

OP here. Thanks all. I'll think of something.

It wont work to tie the load and ground pins together because they're at the exact same potential. It also wound't blow a fuse because there would be no real connection to ground.
You have to run a separate ground wire to illuminate the switch.

Toddupton wrote:
Yes that is a problem and will blow the fuse. Going to need a ground to make it work.

It probably will not blow a fuse in this case, but the light on the switch will not work. The light (an LED probably, but it could be a little incandescent bulb) would be connected between the load connection and the ground connection, and both switched together to the hot connection by the switch. If you tie the ground to the load connection, it's just connecting both leads from the light to the same place.

Think of it this way. The new illuminated switch is basically the same as the old switch with an added LED. Once the switch is moved to the On position, the load is now hot but for the LED to be lit, it requires the ground to complete the circuit specific for that LED.

The ground for that new switch does not have to be an independent ground as you can tie into another ground nearby. Maybe there is a 12V light where you can use that ground? Also, if yours is like mine where there is a "reset" LED in the same switch plate, there is a ground there you can use. You will just need to test which is the ground wire.

Yes that is a problem and will blow the fuse. Going to need a ground to make it work.