I have an '83, but I believe the glowplugs are the same for later engines as well. They are 12V plugs. You can feed them 12V like any other plug and they'll run just fine. The reason we call them "6V" plugs is that the glowplug controller only uses 12V when it's really cold out; most of the time, it gives them half-voltage. Half-voltage is accomplished with a resistor pack and a separate (but apparently identical) relay. I bypassed my glowplug controller and resistor, and run a manual switch to the 12V relay. It's been like that for over a year, on the same plugs, and works great.

You can clean and fix your controller, too. Spiders living inside, rats eating the wiring, or just plain loose/corroded contacts (Mitsubishi seems to be more prone to this than other brands). However, the system also relies on a two-prong coolant temperature sensor, which... I don't remember exactly what the case was, it was either impossible to find or just too expensive. In my case, the sensor went out, my parts engines didn't work any better, so I converted to manual glow control, aftermarket mechanical temperature gauge, and haven't looked back.