So I did it yesterday, got some good copper wire, a Ford starter solenoid from a 1970's Big Block, a nice illuminated spring loaded toggle switch, and some good electrical connectors from the electrical supply house.
I can't take credit for the design but there are a few things I learned here. Being an electrician, I know the importance of a good solid electrical connection. There's no substitute when doing anything electrical, never cheap out and buy rinky dink connectors. If using stake-on fork or ring terminals, buy a GOOD set of crimpers don't hack it in with cheapo pliers.
Anyway, I followed some info I got in one of the post here, and ran a new number 6 copper wire from one side of the new solenoid direct from the battery. Then from the other side of the solenoid to the factory 1988 glow plug controller. Use a 1/2 inch wrench to remove the 2 little grey wires on the load side of the factory controller. CLEAN them with a small file, then install your brand new wire from the solenoid to this controller then reinstall the 2 grey leads which feed your glow plugs... make sure you have a good lock washer in there.
I ran a number 12 stranded wire into the cab of the truck for the switch with an inline 20 amp fuse. Come back off the switch from the ACC thats stamped on the switch to the new solenoid small terminal marked "S". Leave the one marked "I" alone. The old ford solenoids are grounded through the base of the solenoid so if you mount this against a good grounded piece of metal under the hood there's no need to run a ground back to the battery. The BEST thing to do here would be to find a good grounded piece of metal accesible from both sides to nut and bolt the solenoid to. Then run a number 12 awg wire from one of the mounting bolts direct back to the battery. Make sure you ground the switch inside the cab if neccesary.This is simple run a new number 12 awg wire from the ground terminal on the switch to a nice shiny spot that you just scraped with a file under the dash and connect a nice new ring terminal to finish it off. Guess what, when you just strip the wire about an inch and crank a screw down on it thats hack, give yourself a good ground.
Now comes the good part and a comparison too. Turn on ignition, let factory glow controller do its thing, but watch the volt guage on the dash. It jumps down quite a bit. After factory glow cuts out bang your new switch and watch the meter again, it comes down half as much, this is EXACTLY what you want. This also allows you to glow your plugs before even turning on your ignition. But wait, the way we wired it the WAIT light on the dash still comes up Nice.
Its a fairly cold day today in Rhode Island, about 27 this morning when I started up the dually, it never started so good. I glowed it with AC60g's for a while and it started up within 2 revolutions, with zero smoke, what a blessing. Ill post some pics in about an hour or so. Total time to install, about a careful hour. And don't forget to be careful with the factory glow controller when working on it, one side of it has 12 volts waiting to bite you hard at all times if you don't disconnect your batteries. Hope this helps.