I went to start my D6C after it had been sitting for a couple of weeks. deader than a doornail. disconcerting that the big batteries would die after only a couple of weeks. charged them up, still dead. eventually noticed that the circuit breaker in the panel had popped. reset it and it popped again, in both the heat and start positions. that means bad switch, right? found a NOS switch still  in the box. when it came I put the meter on to make sure it was ok. it was conducting heat in both the heat and start positions. that sounded like a good idea to have heat on while cranking but it didn't seem right. I googled heat/start switch and immediately came up with a club thread from 11 years ago in which EDT66SS was having trouble with his electrical. Turned out his problem was a bad battery disconnect, but in the thread was this from Bruce P:

IF, the breaker is tripped AND it continues to trip when you try to turn the glow plugs on, or, turn the starter over. Unhook the main glow plug lead where it connects to the conduit at the rear of the engine. If it no longer trips, then you may have a short in the metal conduit somewhere.
Over time vibaration will wear a hole in a wire.
This is what my D6C did last fall and nearly drove me silly (er). What I couldn't understand was why it would trip when I put the switch to START, untill I realised my switch keeps the glowplugs on in the start position. The local dealer told me some of the switchs are that way. Anyhow, new glowplug harness, all better.

Bingo! my switch is supposed to heat in the start position AND unpluigging the glow plug connection solved the problem. my machine starts easy without the heat so i'll just leave the glow plugs disconnected.
So many thanks to Bruce P and EDT66SS, i couldn't have solved the problem without you as i was fixated on the idea that the heat and start positions were isolated from each other.
what a great club!
 

Good deal: I had a similar situation with one of my D5's. I accidentally arced the starter while fumbling with a repair; whoopsie, I thought I had fried something! It turned out that the breaker button (mine was blue btw) tripped. Talk about a sigh of relief. Admittedly, I was taking the tractor apart to see what I had messed up. Duh,,,,,what that blue thingy?
Nothing like learning from past experiences, however, I prefer to learn from the boo boo's of others!
I do not see the point of having both functions at the same time; makes no sense. There are some tractors here that have only start position/running. I wish to think that they do not have any glow plugs.
The rail for wiring can get crusty as mentioned; Good point about checking it for broken/chaffed wires.
Interesting topic for sure. Yes, there are some others that have had good things to share. The Discussion page is a valuable source of information for sure. JM

Turned out the problem was a shorted glow plug and in one of the most difficult spots to get to. but it starts fine on 5 plugs so i'll leave it that way.
could have saved a lot of hassle had i gone about it more methodically but the new rail looks good and it was a good learning experience, not the least of which was coming across a recommendation in the shop manual to keep the heat on after starting to help smooth it out, i'd always assumed no heat after starting.

Glad you found that helpful.  I’d about forgot about that.  

Bruce P.  

Your post was more than helpful, Bruce, it was a life saver. I like the machine, it's powerful, responsive, maneuverable, but it has some unique features that without info from the club members such as yourself it would probably just be sitting.