GP troubles. controller or plugs?

[vwbuge]

The 300SD has been a bit tough to start and a little rough idle for the first couple seconds on cold mornings. GP light comes on as usual. Except for this morning.

I went out to start and GP light came on but car would not start. Just cranked and cranked not even firing on one of the cylinders. After about 5 minutes and quite a few tries, the car started and idled very rough with a lot of smoke. I got home and this afternoon went to start the car again. No GP light at all.

I had a spare controller and swapped it to no avail. I installed new GP a few years ago. So now I need to troubleshoot but I cannot find anything in the DIY section. I also searched but came up with no straightforward answers. How do I test the GP and how do I test the controller? Is there a fuse for the system? Is my car different being an '85?

Thanks

[newtodiesel]

http://www.dieselgiant.com/glowplugrepair.htm

[vwbuge]

So my GPs finally came. Installed without a hitch. I had a spare controller in the trunk and ended up swapping/testing each one. Turns out they are BOTH good. Starts like a champ now.

However, when installing I noticed the wire coming from the back of the harness (near firewall) is just hanging there. There are two wires after the the last GP. One goes to some kind of switch near the bottom of the motor. The other is just hanging there and looked like it broke off somewhere. Left me stumped because the system seems to work great but just puzzled where this went.