I have a 77 300D. It has the larger size I am assuming loop style glow plugs, and the small relay up on the firewall. I have not removed the GP, but they ohm out ok in the head.

Does this system also glow for about 30 seconds, like the one in the 83, or only as long as the light is on? Having starting issues due to the cold weather, everything seems ok, except the engine is worn and needs changed. Any other keys to sweet talk this engine into starting when it is on the cold side?

I need to get about another month ot of this one so I have time to swap it.

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83 300SD Dark Silver Dark brown inside

77 shouldn't have a relay on the firewall. That's the fuse. Relay is under the driver's kick panel. I would switch to pencil plugs. Makes a substantial difference in cold starts. I would not buy the kit, just retrofit pencil plugs, make the loop wires yourself, disconnect the ground wire at the front and hook up the back plug the same way the current plug is attached to the fuse box. Also use synthetic oil to improve cold starts. In addition, you could add the turbo engine starter which is better than the NA starter from what I have read.

How did you ohm out our plugs? You don't test loop plugs the same way as pencil plugs. You check loop plugs for continuity thru the loop. Do you have heavy squiggly wires connecting the plugs?

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

The plugs are larger than the ones in the 83. But only have one wire, and the front wilre that grounds to the block is not connected. So I ohmed them he same as the 83. Guess the conversion has already been done? The #5 seems to be the control plug, it is wired to a small square box on the fire wall, The other 4 are also, but they are chained together, not #5.
The GP system works, it is just that it is cold and the engine needs to be changed. It leaks oil like crazy out of the rear main.
I will change the engine with one from another 83 when I get a chance. I will also change the GP system over.

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83 300SD Dark Silver Dark brown inside

Sounds like you have pencil plugs already. It should continue glowing after the light is out. You should be able to hear the relay click off. Does the small box the plugs are wired to on the firewall have an 80 amp fuse inside. If so, that's probably just the fuse box and the original relay is still functioning inside the car.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Concerning upgrading old loop style 21mm glow plugs to pencil/Duraterm.
My experience with the upgrade was night and day . The car[ an old 79TD with 250K and real poor compression] will start in about 7 seconds at twenty degrees F . It fires up quicker cold than warm !

blackestate :
If your car upgrade glow plug set was properly installed there should be another larger relay in the engine compartment for the first four glow plugs .It should have the #'s 0 281 003 005 on it with a five pin harness attached to it and two other wires coming off it, one of them going to the first four glow plugs. If they upgraded it but mounted the relay inside the car it is not operating the after glow function properly . The upgraded relay has a temperature sensor in it that is tripped off by the engine heat . The after glow will last up to three minutes or when the engine compartment reaches a certain temperature which ever comes first .

If your car has a second [ not the coolant gauge sensor] temperature sensor on the head that went to the old relay , it is no longer used for the new one . It seems you can only get four cylinder upgrade kits these days and to upgrade a five cylinder YOU MUST [as stated in the kit instructions] install a seperate relay for the fifth plug ] Either a Bosch 0 332 002 156 or a TYCO BR-5000 .It seems all suppliers [ the ones for this site included!]just tell you to order a fifth plug, but you do need the extra relay . Tyco I guess makes or is a Bosch manufacturer .This is a 75 amp high current relay . Here are the full specs of the relay.

http://www.texasindustrialelectric.com/relays_0332002156.asp

It got me wondering if these new Duraterm glow plugs could be a little much for an old relay .I think they draw a lot of current in those first eight seconds . One thing Bosch says to do no matter is always check to make sure the timer function of the relay is working properly[I think they mean that it is actually turning off!] when you replace glow plugs .

If you ever bought one of these kits and were wondering the importance of the little bulb that comes with it . It is an "LED" replacement light to replace your glow plug dash indicator light to allow more voltage to go to the glow plugs .

Other things to do when working on making your car start easier is to have your battery tested[any auto parts store should do this for you free] and make sure your getting enough voltage and cold cranking amps .It must be in very good condition ! If not, buy the biggest baddest battery you can find . I have an Optima 850 cold cranking amp battery and it is a huge difference .
Old sluggish starter ? Replace.
Old corroded battery cables ? Replace
Old corroded connections? Clean .

Good Luck ! Spike.

I have the kit - does anyone know where the "50" and "15" wires are supposed to go on the control box harness?

Thats an unusual name--Are you from Arkansas