Updating glow plug system
 

A friend has already installed the new style plugs in his '79 300CD. Can we get a glow plug wiring harness out of a newer 123 or even 126 chasis and use it to run the GPs? How would we connect that harness to the older style one in the CD?

If you are using "fast" pencil style plugs in that older engine that had used "series" style? then yes. you need a diagram of both systems to see where to graft-in the new signal wires.

Did you get the new GP relay (kit) If not all you need too do is disconnect the ground, use a 80 amp strip fuse instead of the 50 amp and your good too go. Just glow for 5 to 10 seconds.

When I put the pencil style plugs in the 77 300d, I just disconnected the ground, hooked the first one to the same wire the first series plug was connected to and put jumper wires between the plugs. Been working fine this way for years.

Yes that is correct.

I think he did get the relay, except that he ordered the wrong one and it was for the 4 cyl; not the 5, so he can't use it.

I am "assuming" that if we can locate a hot wire that the relay will take care of all switching/timing issues.

Failing this, has anyone installed a manual " push top start" momentary contact switch to run the glow plugs? I would use a relay to ahndle the heavy current; the switch would only carry a very light current.
( I have done this on my F250 Diesel--their GP controller was a menace. Ford installed 6 volt plugs in a 12V system to get faster starting. The controller was supposed to cycle the plugs to keep them from frying on 12V. They would only tolerate about 15 seconds before burning out. I saw my controller comeone while driving down the road at 50mph with a warm engine. They were burnt out before I could even stop. I switch to 12V GP and a manual push button, and haven't had any problems in 6 years or so. But this is a Ford--do Mercedes folk tolerate such re-engineering of these machines?:)

Where did you get your plugs, and how much did you pay? I have been searching for a set to replace my damaged ones... kinda hard to get for low $$. "kit" and "set" prices are all I can find... I only need the plugs. not the wires not the relay kit... arrgh!
John

Which plugs do you need? The Bosch part number 80006 pencil type can be had at AutoZone for 9.99 each.

80006 are the small body plugs, I need the large body plugs... for the 79 motor that this thread is talking about... the upgrades from the series set.
John

I use a 15 amp push button switch on my 79, I love it that way, I don't need no stinken relay to figure out how long too glow:) I run the hot wire through the indicator light and use a Ford truck solenoid.

Do you or anyone else who has made this modification have a part number?

You don't need to do anything more than hook the first plug up to the same hot wire that energized the old plugs and then put jumper wires from plug to plug. My kit came with jumper wires but they would be very simple to make.

loop -> pencil, 1980 300D
 

Hi--Thanks for all of the great sharing of information!

One day a couple of weeks ago on my 1980 300D, I had a flashing gp light on the dash and no start--not even crankable.

I took the opportunity to get the pencil style (large body) plugs, but wonder if it's actually the relay. Before I test the new glow plugs, I'd like to make sure I'm clear on a few points:

1. Disconnect the ground strap (at front of engine) from glow plug post
2. Use some heavy insulated wire to make jumpers between plugs (to replace the stiff wires)
3. Replace 50 amp fuse with 80 amp fuse? (necessary?)

And then I guess I'll see if my problem was the plugs or something with the relay; I'm thinking it might be the relay since I didn't get a crank. If that's the case, I'd be interested in a "manual" glow period with a switch on the dash, like Stevo--and so a 15 amp switch will be adequate?

Thanks!

Yes, except I did not replace the original fuse in my 77 300d and it's still working fine 3 yrs later.

If you go the manual switch route, you'll also need a starter solenoid. I would put an 80 amp fuse in there or at least have one in the glove box. I didn't go to the 80 amp right away but its proly a good idea.