1984 300d. Ok, checked glow plugs they seem good. Fuse in relay good. Power good to relay box. No power to the 5 pins in relay box when key is turned. When engine turns over get power to the 5 pins in relay. Car starts hard but runs fine, but its been warm here , the glow plug light no longer lights. Any ideas? Don't want to get a relay if I don't have to. Thanx Jimmy

Did you check the fuse upstream of the relay? I don't know which fuse that is in a W123. If you haven't done so in a few years, replace (don't bother inspecting) all the fuses in the fuse box. Who knows what other problem you'll fix

Sixto

The relay box fuse has been known to go on other cars. It would be good if this was your problem.

__________________
Ralph

1985 300D Turbo, CA model
248,650 miles and counting...

Where you say “Fuse in relay good” -- I have found the fuse on the relay to be defective even though it looks good with a meter [ continuity and zero voltage drop] but later found it had failed due to “ embrittlement ” which makes it work intermittently and even sensitive to temperature. I recommend you replace this ~$2 part and get a spare too. You might just find this solves your problem.

Where you say “When engine turns over get power to the 5 pins in relay ” – This is not entirely inconsistent with a fuse that has an “ embrittlement ” failure… and keep in mind that the relay is designed to continue powering the glow plugs for up to about 1 minute total time… even after the engine has started.

Where “SIXTO” says “Did you check the fuse upstream of the relay” – The glow plug relay fuse is rated ~80 amps and to the best of my knowledge IF your relay has such a flat [~80A] fuse, there would be no other fuse "upstream"… certainly none inside the fuse box on the firewall… there are none there high enough in value to supply the 50-70 amp load of the relay and glow plugs!

Try throwing a new 80A fuse at the relay… it’s cheap! You need a spare anyhow... and I would not be surprised if the old one breaks in half during removal ! What's your alturnative... big buck$ for a new relay?

Sam

One of the relay wires goes to fuse 12 but it hooks upstream of that fuse. It's not a fused line.

Is the glow circuit tied into the neutral start switch?

Sixto

Sixto,

GP relay is not connected to the Nuetral switch because the relay will work even if the shifter is not in nuetral or park.

P E H

Okay. On some models there's a wire that goes to the NSS. I don't know what it's for.

Sixto

replaced fuse no good. Swapped relay with friend, glow plugs work. Guess I gotta get a relay. Thanx 4 your help Jimmy

See if any steps in the pictorial can help you at all.

http://dieselgiant.com/glowplugrepair.htm

__________________
1981 300D 147k
1998 VW Jetta Tdi 320k
2001 Dodge Ram 2500 141k
1979 300D 234k (sold)
1984 300D "Astor" 262k(sold)
Mercedes How-To and Repair Pictorials
I love the smell of diesel smoke in my hair

.......keep in mind that the relay shuts down immediately when the key is turned to the #3 position (start)........no matter how long it has been engaged.

The only exception are for those folks who have spent the money and installed the afterglow relay kit with replacement glow plugs. Most of us have not.


........careful on providing information that's grossly inaccurate. We've had a spate of this recently........

You can check for an "embrittlement" fuse failure with a meter. Assuming that at least one glow plug is working, measure the voltage drop across the 80A fuse with your meter while the GP relay is active. The voltage should be under 1 volt for a good fuse.

But you should still keep a spare fuse in the tool kit.

__________________
Ron Schroeder
'85 300 Turbo Diesel 2 tank WVO
'83 300 Turbo Diesel 2 tank WVO
Some former WVO vehicles since ~1980:
'83 Mercedes 240D
'80 Audi 4000D
'83 ISUZU Pup
'70 SAAB 99 with Kubota diesel
'76 Honda Civic with Kubota diesel
'86 Golf
Several diesel generators
All with 2 tank WVO conversion
LI NY