jbach36; I have a 92 300SD and I have the same box. There is no visual fuse, is an internal relay due to the fact of afterglow feature. System the activates on cold weather. Glowplugs need full battery charge or they will not came on. Check dieselgiant.com for trouble shooting procedures, you will need a multimeter tester. (skip the step of the fuse). Good luck Victor vmcastillo@verizon.net

thats what im seeing

basstrip you have w140 which didnt have the fuse

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1986 300SDL, 211K,Dealership serviced its whole life
1991 190E 2.6(120k)
1983 300D(300k)
1977 300D(211k)

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Haven't been online for a few weeks now, getting ready to move to Kentucky. Yesterday a problem popped up and never went away.

No fuse on my relay either.

Yesterday, typically starting cold, glow plug dash light would come on and stay on after starting.

Sometimes it would not come on, but it would still start.

Read a while on the internet & decided to follow a few of the suggestions.

Found glow plug four failed resistance test.

Last thing I did was pull the glow plug relay, take it apart and clean contacts thoroughly with both alcohol and contact cleaner sprayed on thin paper.

Put it back together, added a mickey mouse led, and tried a cold start.
Dash light came on, dash light went out, I started the car.

Dash light went out. I checked outside and the LED was bright red.

I watched for about two minutes and it went out.

Checked inside and the dash light was back on. Checked LED again and it was still off. LED shows me the glow plugs are heating or not.

I'll update in a few days once I learn more.

Attached Thumbnails

         

When one plug is bad, you won’t get the preglow light when you start. Once the engine is running, the light comes on and doesn’t go out. Now you know the secret code, replace your plug and be happy.

The light is not consistent.

Sometimes, when cold, it comes on like normal and goes off after a little while, then comes back on and stays on.

Other times, when cold, it does not light but starts easily. After a while light comes on and stays on.

Hopefully the glow plug relay is ok, time will tell, probably won't attempt #4 glow plug change until sometime this winter in central Kentucky. At least the glow plugs aren't heating all the time.

Thanks for your comment.