Originally Posted by macdoe

Thank you, on the stock g.p relay there is the large connector going to the g.p's (which we rebuilt) and the large single 8 guage wire for power and then there is a smaller plug....what is the smaller plug for and where does it go?

Originally Posted by OM617YOTA

I was perusing the Ether thread and a couple other cold start and glow plug threads and I got to wondering: What is the stock MBZ glow plug wiring like?

I'm an auto lighting aficionado. I have relays and upgraded wiring on the headlights of just about all my vehicles. With a halogen bulb, a 10% drop in voltage(very very easy to surpass with undersized corroded wiring) causes a 46% drop in light output.

Are glow plugs the same way? Could undersized or corroded wiring be causing some people to have cold starting issues? Great glow plugs won't work properly if they're not being fed properly. My 617 in my truck didn't come with the car or stock glow plug wiring, I built my own glow plug wiring harness. It's a 4AWG cable running from the battery positive post to a 100 amp fuse, then to a Ford starter solenoid, then out to the engine. From that 4AWG cable, 10 AWG wires run less than a foot to each individual glow plug. I'll have to measure my voltage drop with the glow plugs on when I get home.


This might be something to look into - I'm kind of shooting in the dark here, having no idea what a stock MBZ glow plug harness is like, it could be built massive overkill. On the other hand, it doesn't matter if the battery is at 12.7 volts and your glow plugs are new if your glow plugs are only getting 10 volts or less.

Originally Posted by Diesel911

The crimped on Eyes on the Glow Plug ends of the Wires likely corrode as they do on other applications.

For the Stock Wires you can clean the exterior and if you can get to the area where the crimp is you can Solder them good and that usually restores a good contact.

Originally Posted by funola

Have you looked at the glow plug circuit diagram in the FSM? The small connector is for control and cluster glow indicator. Why did you rebuild the wiring? The stock wiring is well designed and well built, nothing much goes wrong with it other than corrosion in the mating contacts which is easily rectified by proper cleaning. The terminals are soldered (not crimped) so corrosion there should not be a problem.

Originally Posted by macdoe

Nope, have'nt looked at the manual...I am not sure that my copy even has that section(doubt it) I have the internet copy. As mentioned above... the harness was redone due to it being old ,greasy and having at least one broken and probably more dried out crusty wires, that I did'nt want to worry about.in these temperatures. Not at all reaching considering the harness has been sitting next to the cylinder head for over 25 years.
So for the sake of your post Funola, I went and checked each piece of individual wire from the dissected factory wiring harness....and you are correct...each pce seemed to be good....could have got away with just changing this one lug on the factory harness. Lots of green corrosion....are you sure the eyes for the glow plug end are soldered? Mine look like they are double crimpped?? Overall we are glad to not have to woory about it in the cold, it is now more flexible, but even the new harness was abit difficult to bend the longer we were outside with it, had to work fast in these temps.
The ten guage wire was difficult to get into the connector at the relay end.