GM-GMC: manual glow plug control, chev blazer, glow plugs

Question
I have a 1990 Chev Blazer with a 6.2 diesel. The glow plug controller quit working and the previous owner wired a switch between the battery and the closest glow plug wire. I don't like this, I think there is too much power going thru the switch.  Which is the right wire on the gp controller to use. The other side of the switch will be grounded.  Should it be a splice or cut right off.

Answer
If you have the OEM glow plug controller, all you can do is send it a false signal that the engine is cold (and make the glow plugs cycle on and off when the engine is warm, just as they are supposed to do when it is cold).  You cannot manually control the glow plugs with the OEM controller.

Here is a URL that shows the 1985 and older glow plug relay:  http://www.rockauto.com/ref/ACDelco/Detail.html?D1777.jpg

If you want to manually control your glow plugs, you will have to install one of these relays and wire it with a switch to send power to one of the small terminals.  The other small terminal is grounded.  The glow plug power wires connect to the big terminals, the same way as the controller on your vehicle should have them wired now.

Manual control of the glow plugs requires that the glow plugs be self-limiting.  AC-60G or equivalent glow plugs must be installed to prevent overheating, burn out, and tip swelling.