Bosch Duraterm Plug Upgrade Kit
 

I got the kit, from mbparts.com It's the kit with 4 plugs, a relay, and a few short jumper wires.

I am trying to do the install, and the instructions are helpful for the most part...

I have a 1977, 240d 123.123


It tells you,
brown to terminal 31(earth)
Read to terminal 15-Fuse Box
Black to 50-Fuse Box, or starter.

Obviously, I know where Brown goes... And I can find the starter ;)

Where the heck is Terminal 15??!? The fuse box goes Up to 14..

Secondary, if I wanted to connect the starter in the fuse box, where would 50 be?

Any guidance would be helpful

The glow plug timer has terminals identified as 15 & 50. (Smaller pins on the top.)
I have no experience with the conversion, so that information may or may not be helpful.

That does help some, it would make sense since this replaces the old glow plug system.


One think I have had trouble with is identifying the old relay/timer. Anyone have a picture to show where it should be?

I've been told its a silver box under the dash, I see 2 or 3..

When I upgraded my 77 300d, I saw no reason to replace the OE relay and timer. I put in the new plugs, wired the one nearest the firewall the same way the old set was, disconnected the ground wire from the front plug and put the jumper wires between the new plugs. Been working fine that way for 6 yrs.

Its a large silver relay bolted to the steering column under the dash. Should have an 8 wire connector on the firewall side of the relay.
Here's a pic of the general area with the relay removed.
http://www.neptune242.com/benz/misc/gptimer.jpg
The wires you can see loose are from the new gp controller. I didn't feel like cutting and splicing and wanted to make the new controller easily removable, so I found a spare 8 terminal wiring connector, soldered terminals to the gp kit wiring, and connected it to the existing glow plug wiring in place of the old relay. The pic was taken so I could remember which wires went where, after I took this I added the connector and it now looks like a shorter version of the wiring connection to the left of it. Looks clean and factory, but works so much better.
Her 77 has been using the upgraded glowplugs and controller, wired like this for over two years now without a single problem. We couldn't be happier.

On German cars, "15" designates an IGNITION switched "+".

awesome, thanks for all the help! I soldered the wires into the connector (really hard to do when its 20 deg outside haha )

My original goal was to keep everything intact, but due to me not wanting to run a new DC line from the battery, I jumped the fat Purple, and fat Red wires that were connected to the old relay I can get the pin #'s if your interested..

Soon as I can get back outside I'm going to give it a test it out.. i'll post my results

Can someone explain the advantage of replacing the original relay when replacing the loop plugs with pencil plugs? I couldn't see why it was necessary.

I have to find out the specifics, the main benefit would be the afterglow feature, not entirely sure if this relay has it (not specifically mentioned). It is also designed for this style plug so there may be other small differences.

The kit I purchased came with the relay, so I figure why not use it. (Usually quite expensive on its own).

In our case the biggest motivation was the fact that the entire new style kit (relay, plugs, and wiring) was cheaper than just the relay for the 77 (ours failed on, frying a couple plugs too).
I figured the new style relay was required to run the pencil plugs, but perhaps the old relay can be made to work. To install the new relay I had to run four wires to the old relay location to tap into the existing wiring (ignition switched power, output to glow plug light, ground, and I forget the last one, probably starter). In the engine bay I got to ditch the old resistance wires for the series-wired loop plugs, and run a power wire directly to the battery (via fuse) for the plugs.
The new relay does not use the temp sender in the head, it uses the ambient air temp of the engine compartment (ie where the relay is) to determine how long to glow after starting. As I understood the system, our original 77 relay didn't glow after starting. That alone made a big difference.
For us the benefit was the combo of the more effective and reliable pencil plugs, more advanced glow plug controller (afterglowing), and the fact that the whole kit cost less than replacing the original relay and a couple melted loop plugs. Honestly its been the most beneficial hour or two I spent working on the car.

I bought the whole kit when I was upgrading my 77300d from loop to pencil. Once I got it, I couldn't figure out why a new relay was necessary so I just tied in the first pencil plug the same way as the old loop plug and have been using the old relay. Kept the new one as a spare. I guess the afterglow does provide some advantage.
I assume the replacement relay will also serve to substitute for OE relays on the later pencil plug engines??