I have a 79 240D I just bought and I wanted to see what type of glowplugs were in it. I was thinking I had the older loop style glow plugs and I was correct. But to my dismay I discovered one was an older style Autolite glowplug and three were newer looking Autolite glowplug. Unacceptable. I want to upgrade to bosch pencil type glow plugs. My questions are:

1. Will the pencil type fit into a 79 240D?

2. Will I need to wire them differently?

The way they are wired now I belive is in series becaues the last one is grounded with a grounding strap to the head. The power goes from the battery to the manual glow switch to the glowplug #4, 3, 2, 1 and each one is connected with a coat hanger looking wire that is specially bent and is flexible (looks like a part, not a jimmy-rigged wire job)

Thanks in advance for the responses, I am new to diesel mercedes as this is my first one and I have only owned it for a few weeks...

Loop plugs are series, pencil plugs are wired in parallel, so yes it will be necessary to re-wire. Regular late model pencil plugs don't fit the loop plug holes, but there are kits on the market to facilitate the conversion.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

Phil sells the correct BOSCH large body pencil plugs here on the forum. click the buy parts section and call Phil.
google large body bosch glow plugs to find the part number...
your existing relay and body connector, IF its working will handle the pencils just fine.
you will need to build a wiring harness to the plugs!

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Your wiring and other questions will be answered below:
Repair Links
http://www.peachparts.com/shopforum/diy-links-parts-category/

http://www.peachparts.com/Wikka/DoItYourSelf

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84 300D, 82 Volvo 244Gl Diesel