In my 1987 300TD I replaced all the 'ice-cube' relays behind the fuse block. I also refreshed all my fuses with true copper fuses. Before doing this work my glow plug light in my gauge cluster came on like normal, afterward it no longer comes on and I don't think the plugs are glowing based on how rough it starts.

I put the old relays back without any effect. The fuse strip in the glow plug relay is fine.

Is there anything I could have messed in the glow plug circuit by replacing the relays and fuses?

Check that you have 12V at both ends of the 80A fuse. That circuit is always live. Remove and reinstall the 80A fuse to make sure it’s not cracked and just making contact.

There are 4 small wires to the glow relay - one is ground, one gets 12V when you turn the key to run, the famous purple wire gets 12V(?) when you turn the key to start, the last one goes to the glow light in the dash. Hopefully this is enough to figure out what’s wrong.

Sixto
98 E320s sedan and wagon
02 C320 wagon

I don't think you have messed up anything. Check the glow plugs for continuity. It is possible that one glow plug gave out. You probably were running on 5 GP, the GP light still comes on with 5, but not 4. Now the GP light wouldn't come on with 4. It would be very difficult for car to start with 0 GP on.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

I went ahead and pulled the intake manifold, reamed the GP holes and replaced with new GP's. Light is back and it's starting much smoother now.

I didn't check for GP continuity to identify which plugs were faulty since I wanted to replace them all. Since I have a baseline of new plugs now I will use that method if/when I have problems in the future.

Good to know that the dash light will still come on with one glow plug out but will stop working when a second goes out. New and useful info to me

Talk about coincidence. The odds of another glow plug calling it a day are very long. In such a small time frame. I would still check them for continuity though. Just to make sure.