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Old 01-18-2011, 07:31 PM
79Mercy's Avatar
Registered User
Join Date: Mar 2008
Location: Florida
Posts: 4,128
Loop Glowplug and Relay Upgrade

Waiting 45-50 seconds every morning for the old loop plugs was a bit excessive. On the W115 300D's the original relay will NOT work with the parallel pencil plugs(Bosch Duraterm #80035), and i did NOT want to have a rigged push button under the dash and a ford starter relay to operate them...i wanted to retain the original function of the system.

So I decided i would get a complete wire harness and relay from a turbodiesel W123 or W126 and install it in my W115 so that I could use the pencil glowplugs.

Here is how it is wired:

The turbodiesel relay:
PIN LA- glowplug light
PIN 31- ground wire
PIN 50- violet wire(starter signal wire, same color at old harness)
PIN 15- relay wire(black/blue/green wire, at original harness)
12V constant from the battery

So i ran a harness from the turbodiesel relay under the hood to the old harness at the original relay under the dash and spliced into 2 those wires(blue/green/black, violet).

Then I ran the GP light wire up the light socket, and grounded the other side of the light bulb.

Then i put in the glow plug wire harness that goes from the relay to each GP, which i pulled from a 1984 300SD at the junkyard.

Im very happy with how this updated system works, it is wired up exactly as it should be and nothing was rigged. None of the original wiring was damaged and I could return the system back to the stock loop plugs and relay system very easily.

The car starts up great when the GP light goes off(about 4 seconds). Never has the car started so quickly. I plan to make a movie tomorrow morning to compare to my old cold start video when it had loop plugs.

Here are some pictures:

1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles
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Old 01-18-2011, 09:12 PM
Diesel911's Avatar
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Join Date: Sep 2007
Location: Long Beach,CA
Posts: 23,207
You have the best idea if you want to keep the system as stock as possible.

Your idea is a better option than buying the Glow Plug Upgrade Kit that comes with the Special Glow Plug Relay because if the Kit Relay went bad; where would you get a new one and a what cost?

Some what in between what you mentioned the Ford Starter Solenoid could be used in conjunction with the same circuit and Wire that would turn your Old Stock Glow Plug Relay on.
That would allow you to use your Key in the normal Glow Position but the Glow plug Light would not work. (The light could be wired in but would not turn itself off.)

If you wanted the Solenoid to be on while the Engine is cranking as it does with the stock Glow Plug Relay it could also be hooked up to the Violet (Purple?) wire that connects in your case to the Starter Motor Solenoid.
84 300D, 82 Volvo 244Gl Diesel
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Old 02-06-2011, 10:51 PM
euroamg's Avatar
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Join Date: Aug 2003
Location: BC,WA
Posts: 573
Thats a great ugrade... I have to do that on the 300d too. Takes forever to glow the old
'76 300D '82 230CE
'84 300DT '90 300TE
'91 300D 2.5
'86 300D 5 speed
'86 250D 5 speed
'90 300E 24 '88 560SEC
300TE euro 5 speed X2
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Old 04-09-2012, 05:54 PM
whunter's Avatar
Join Date: Dec 2003
Location: Metro Detroit, Michigan
Posts: 17,350

To get you on the road quick.

Homemade: Loop to pencil style glow plug conversion

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Old 04-10-2012, 09:54 AM
Fold on dotted line
Join Date: Aug 2007
Location: SE Mich
Posts: 2,944
Originally Posted by whunter View Post
By any chance, does anyone know the NAPA or Ford part number for this? Am asking because I bet there are some inferior designs of solenoids that should not be used.
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1950 170SD
1951 Citroen 11BN
1953 Citroen 11BNF limo
1953 220a project
1959 180D
1960 190D
1960 Borgward Isabella TS 2dr
1983 240D daily driver
1983 380SL
1990 350SDL daily driver alt
3 x Citroen DS21M, down from 5
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