123 - my relay is supposed to be under the dash as well. I have the series plugs, the 50amp fuse on the firewall. My limited manual says "Glow Plug Timer Relay - driver's side under dash". However I have not found this relay - can you tell me where it is located under there? I'm probably looking right at it and thinking it's something else. Thanks again...

The relay on my 77 300d is located right above the brake pedal and is screw mounted not a plug in. Actually is mounted to a support bracket.Remove screw before you unplug it. Silver in colour and about 3'' high 3'' deep perhaps 1 and 1/4 inches thick. These measurements are just from memory of when I changed mine so beware but the location is correct. You of course have to remove plastic or fibre panel above pedals to access it. Largest relay type device in that area as well if I remember correctly.

I found out that my starting problems were a result of a bad relay. Had enough of all the testing and diagnostics - just hot wired the plugs by connecting an 8-gauge wire to the postive battery terminal and the other end to the fuse. Plugs heated up and the car started immediatly. So I obviously need to get a relay. However I found something odd that doesn't seem right (that I doubt a new relay would fix).

There's been a hot spell where the ambient temp has been about 95F. Like I stated above, the car will start immediatly upon glowing. However the past two days have been around 70F - no matter how many times I heat the plugs the car will not even get close to starting. Today it's 90F again and the car started. I know this probably sounds stupid but it's the truth. I'm in trouble if I need 90 degree days to start this baby!

Any input???

I have a 1975 115 300d. The loop plugs have been replaced with pencil type. The relay went out and was replaced with a starter type button that I mounted on the 'wood' facia on the left just under the instrument cluster. I hold the button in for the count of 10 and the engine fires every time.

It is easy to install the switch. There are 2 very heavy (thick) wires coming from the gp relay. Splice a similar gauge wire into each leg and then into each side of the switch. The relay costs $100 and the starter switch costs about $5.

78 240D 4spd manual

Pretty much all of your symptoms, adjusted valves, tested compression, and troubleshooted ad nauseum .

Roughly two weeks ago converted to parallel pencil types using the kit (not difficult), the starting is superb!

Some members do believe the conversion may have a shorter lifespan though.

Hi Krueger. I am having similar problem. Did you get your's fixed? If so, what was it?

thanks