Homemade: Loop to pencil style glow plug conversion
 

Loop to pencil style glow plug conversion.

Never glow longer than 60 seconds or you risk burning out the glow plugs.

This is a homemade system that works = not for use on show cars.
Note: With minor alteration this circuit can be used on almost any diesel glow plug system.

For safety and durability: You need to use:
* 4 AWG wire for the glow plug circuit
* Make one 8 AWG jumper wire per glow plug, going to the relay.
* 12 AWG wire for the activation circuit

AWG is American Wire Gauge.
The following sites may be useful to bookmark:
Amps and Wire Gauge - 12V Circuit
American wire gauge - Wikipedia, the free encyclopedia

Note: I have seen this system installed (functional) with standard residential wire as an emergency field repair, but do NOT recommend using it.

For safety: You must have two fuses in this circuit:
* 60 AMP fuse as close to the battery as working space allows in the (glow plug feed) primary battery (+) cable.
* 10 AMP fuse where the solenoid activation circuit draws battery power from.
I suggest a 60 AMP fuse with Four glow plugs.

Maxi fuses are color-coded
Red is 50 AMP
Blue is 60 AMP
Clear is 80 AMP

I suggest a spring-loaded push button momentary switch mounted in the knee panel, but have seen household light switches used successfully.

Never glow longer than 60 seconds or you risk burning out the glow plugs.

I use a Ford starter solenoid for convenience, simplicity, and availability.


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Note:
 

A nice potential addition for both diagnosis and safety:

You can add a Maxi fuse block between the relay and glow plugs, loaded with 20 AMP fuses.

This will blow a single fuse any time a glow plug short circuits, alerting you to an issue.
You can quickly and easily pull single fuses for resistance/OHM testing.

maxi fuse block | eBay

On the 123 loop style systems, you can use the original relay and just swap in pencil plugs. Remove the ground wire. Use the hot wire from the glow strip fuse box on the firewall to the last glowplug and then run jumper wires to each successive plug. Operate the system the same way the loop system operated.

Or you could just get the entire timer box from a '78 or later 300D. Run an eight gauge or larger wire from the battery positive to the timer feed, connect a wire to the ignition circuit and be done with it. Connect the leads from the timer to the individual plugs for a 300D and tape up or remove the extra wire for a 240D.

You could even get creative and run a wire for a light in the dash for the "glow" cycle. If I remember correctly there is even a wire to connect to the temp sender to disable the timer when the engine reaches operational temperature but it's not really required.

Use a 50 amp fuse/circuit breaker on the main power feed at the battery connection.

an 80 amp fuse is what MB uses...
the 5 plug system pulls near 100 amps on a cold day for a few seconds...

X2
This would work.

Probably you could use the curved ridged wires as the jumper wires.
Alternate would be to run a metal strip (buz bar) joining the GP's & connect the hot wire to the buz bar. thats what Isuzu do on some of their IDI motors.

All you need then is fittings for the pencil GP's as they are much smaller than the wire GP's.

Pardon my ignorance, but is there any particular reason this mod is recommended?

Answer
 

Yes.
The pencil glow plugs are hotter = better cold starting.

Unfortunately the aftermarket kit is frequently not available, and may be discontinued soon.

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Thanksfor that clarification whunter. I was particularly interested in the comment that the system can be adapted for use with just about any diesel glow plug system. That Ford Solenoid looks like any generic solendoid out there. Makes this a very doable-looking mod for any system by the looks of it.

What kind of kit are you talking about that's not available and maybe discontinued?

BTW, on the topic of GPs, have you considered using 6v or 7v GPs? I ask only because I run a 24V system on my Cruiser and one of the favourite mods by people is to use lower voltage GPs to start those big diesels. I believe mine uses 14V GPs.

There are also those who modify that system using something known as a "Wilson Switch", which is really a manual bypass of the timer. I guess its not so necessary for a Merc diesel.

I just bought the large hole, pencil type glow plugs for my '77 240D and used the stock relay. I just time it myself. Sure starts good now. Been in the low 20's at night and it starts right up.

From What I have read the 1976 Stock Relays cannot handle the updated Glow Plugs; you need another type or Relay. There is some threads on that subject.

DIY Repair Links
DIY Links by Parts Category - PeachParts Mercedes ShopForum

PeachPartsWiki: Do It Yourself Articles - Mercedes Vehicles

I have had this system in my 79 240 for several years and it works well. All I would add to this post is, although you don't have any trouble hearing that Ford solenoid, I ran the switch wire through the amber, GP indicator, dash light. make the system seem more normal:P

I swapped my 78 240D to the Pencil plugs. Didn't change the the fuse or the relay. Just put the plugs in and put new bus wires on and it has worked great for the past few years.

I found a company that makes a 4, 6, and 8 circuit fuse block... rated for 30Amps each circuit!
also, they sell 80, 100, and 150 amp circuit breakers for the cars...

I took pics, and I'll post them with model numbers etc soon...

The 4 port block
https://lh6.googleusercontent.com/-U...119_102657.jpg

the list of part numbers for other blocks
https://lh3.googleusercontent.com/-i...119_102713.jpg

The entire back panel of the 4 port card
https://lh4.googleusercontent.com/-h...119_102741.jpg

and the 80 amp circuit breaker.
https://lh5.googleusercontent.com/-H...119_102757.jpg