Recently I had an issue with the glow plugs in my '79 240D, so I decided to upgrade to the Fast Glow kit from Bosch. Unfortunately, the kit is a generic one for all cars from 1961 to 1985 and the instructions aren't very clear. Since everyone here was too busy talking about Euro bumpers and what MPG they get to answer my questions, I had to figure it out on my own.
The Bosch kit comes with four pencil-style glow plugs, a new Timer module with wiring harness, five plug wires, four hand tighten nuts and a small replacement glow plug light. Nothing in the instructions mentions that last one, but apparently it's an LED replacement.
Here's the included instructions:
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At first I was concerned that there were parts missing, as the instructions talk about an additional relay and fuse, but this is only for 5 cylinder cars.
Figuring out power and ground was straight forward, but 15 and 50 didn't make any sense to me. Looking at the wiring schematics from the FSM very carefully, it begins to clear up:
![Image]()
Looking around the inside line of the Glow Timer box, you'll see the above mentioned numbers 15 and 50, while the outside shows the pin out. With this info, we can now proceed.
First step is to remove the underdash panels to gain access to the existing Glow Timer. I ran the included wiring harness through an unused hole in one of the firewall grommets that run the vacuum lines, and pulled it into the footwell to leave only a bit of slack based on where I was mounting the new module.
Most how-tos online recommend just hooking up the glow plugs to the existing timer, but in my case it was blown, so rather than spend hundreds of dollars for a plug-in replacement, I just used the timer that comes with the kit. The new module has extra functions and is a vast improvement over the old one, allowing much quicker starts and a "afterglow" feature that pulses the plugs during warm up.
Once you've located the old timer, the connector pops right off, and you can remove the plug cover to gain access to the wires. I decided to leave my existing module in place and solder up the included harness to the plug, so that switching back to the old timer would still be possible.
![Image]()
The pins used by the new Glow Timer are:
PIN 1 to PIN 1 - Ground
PIN 3 to PIN 4 - Starter Motor Signal
PIN 4 to PIN 3 - Ignition
PIN 7 to PIN 5 - Glow Plug Light
The other pins on the old harness aren't used by the new module. Another difference is that the new module sits in the engine compartment instead of under the dash, as it has a built-in temp sensor to tell how hot it is under the hood.
![Image]()
I re-used the existing fuse and wire to hook up the plugs, and used the fifth wire in the kit to connect the module to the plugs.
A power wire needs to be run from the battery - in my case I ran it from the starter solenoid:
![Image]()
After checking all my connections, I reconnected the battery and turned the ignition to run, and happily I saw the glow plug light. Button everything back up and you're good to go.
I highly recommend the conversion - the glow plug light rarely stays on longer than the seat belt light now, and the car starts right up and runs excellent.
For Googlers, here's some info on the kit I purchased:
Duraterm-Set - part # 0 250 201955
Glow Plug Timer Module - part # 0 281 003 005
The Bosch kit comes with four pencil-style glow plugs, a new Timer module with wiring harness, five plug wires, four hand tighten nuts and a small replacement glow plug light. Nothing in the instructions mentions that last one, but apparently it's an LED replacement.
Here's the included instructions:
At first I was concerned that there were parts missing, as the instructions talk about an additional relay and fuse, but this is only for 5 cylinder cars.
Figuring out power and ground was straight forward, but 15 and 50 didn't make any sense to me. Looking at the wiring schematics from the FSM very carefully, it begins to clear up:
Looking around the inside line of the Glow Timer box, you'll see the above mentioned numbers 15 and 50, while the outside shows the pin out. With this info, we can now proceed.
First step is to remove the underdash panels to gain access to the existing Glow Timer. I ran the included wiring harness through an unused hole in one of the firewall grommets that run the vacuum lines, and pulled it into the footwell to leave only a bit of slack based on where I was mounting the new module.
Most how-tos online recommend just hooking up the glow plugs to the existing timer, but in my case it was blown, so rather than spend hundreds of dollars for a plug-in replacement, I just used the timer that comes with the kit. The new module has extra functions and is a vast improvement over the old one, allowing much quicker starts and a "afterglow" feature that pulses the plugs during warm up.
Once you've located the old timer, the connector pops right off, and you can remove the plug cover to gain access to the wires. I decided to leave my existing module in place and solder up the included harness to the plug, so that switching back to the old timer would still be possible.
The pins used by the new Glow Timer are:
PIN 1 to PIN 1 - Ground
PIN 3 to PIN 4 - Starter Motor Signal
PIN 4 to PIN 3 - Ignition
PIN 7 to PIN 5 - Glow Plug Light
The other pins on the old harness aren't used by the new module. Another difference is that the new module sits in the engine compartment instead of under the dash, as it has a built-in temp sensor to tell how hot it is under the hood.
I re-used the existing fuse and wire to hook up the plugs, and used the fifth wire in the kit to connect the module to the plugs.
A power wire needs to be run from the battery - in my case I ran it from the starter solenoid:
After checking all my connections, I reconnected the battery and turned the ignition to run, and happily I saw the glow plug light. Button everything back up and you're good to go.
I highly recommend the conversion - the glow plug light rarely stays on longer than the seat belt light now, and the car starts right up and runs excellent.
For Googlers, here's some info on the kit I purchased:
Duraterm-Set - part # 0 250 201955
Glow Plug Timer Module - part # 0 281 003 005
