Originally Posted by funola

Here is my manual glow controller. It is a bad Mercedes unit that's been modified so the cluster glow light comes on whenever the glow plugs are on (i.e. when you push the manual button). There is just one wire that goes into the controller (the small white wire), no wires to the car's harness. Connect the wire to one side of a momentary switch, the other side of switch to switched +12V (need ign. key on to activate glow plugs), or to hot at all times +12 V (battery or headlight switch- no ign. key necessary to glow).

There's no modification to the stock wiring. If you decide you do not want a manual system anymore or when you want to sell the car for example, just buy a new glow controller and swap it out- plug and play.