See this thread:

http://www.peachparts.com/shopforum/diesel-discussion/328382-fast-glow-my-76-240-d.html

You should find what you need here.

I've done the loop to pencil conversion twice now. Both times all I did was remove old plugs and crazy wiggle wires, put in new plugs and new wires, and make sure not to hook up that last grounding wire at the front of the car. Works like a charm

this is correct, if the original glow relay is working, the new relay is not needed, but the loop relay has a 1.5 minute timer, so if something is wrong with it, it can cause the plugs to fail sooner than otherwise.

while the converted pencil plugs appear to be wired in series, they are not. series implies the voltage passes through each plug before reaching the next, this is not the case. voltage only passes through the lug... so electrically, they are parallel wired.
installing a full GP harness from a pencil equipped vehicle would make it simpler to ohm test when plugs begin to fail.

What are your glow times like with the upgraded system?

That is interesting, I was always wondering why on a cold start the timer seemed to last s long time....I usually turn the car over on a cold start before the light goes out....on warm starts the light comes on for a few seconds and go away....I have heard it is not good to glow the pencil plugs longer then 60sec as it can cause premature failure

All the more reason to use a newer relay, since they are supposed to turn off after 30 seconds. I confirmed this with a multimeter when I changed the glow plugs in my 1983 300D.

Are you referring to an afterglow timer, where the plugs stay glowing after the car has started? I thought the older cars didn't have this

The Bosch 0 281 003 005 relay claimed to have after glow doesn't per this:
CCL | Relays >> Glow Plug Relays >> 12v 50A Glow Plug Relay (10-102)

Not sure where kahlil88 got his information of this being an upgrade glow relay, but was a pain to find anything.

Could have sworn I posted the link before. Searched the part number on BenzWorld and found the thread I was referring to: Hooking up the Bosch Duraterm Glow Plug Kit

I went to the junkyard for the parts and found a 1984 300D and 1979 300SD...only the latter still had a glow plug relay, but I pulled the wire harness and part of the wiring that goes through the firewall from each since they were cheap. Interesting seeing the difference...the W123 harness has an extra plug that goes to the intake manifold (ambient air temperature, correct?) and a 4-pin connector that goes thru the firewall (versus the 5-pin in W116), there is also a 2-wire plug that I believe goes to the ignition switch. Each had a thick wire that must be power but couldn't tell where it went.

About 10 seconds at 40 degree outside temp in the morning.

the thick wire goes over to the battery. no fuse, direct to the battery, HEAVY gauge copper wire. at LEAST #8 stranded copper.