When I turn the key to warm up the glow plugs the light is flashing. Very strange. In past experiences with diesel the glowplug coil light either came on or off. I'm not sure if I should check the glowplugs, relay?? it just keeps flashing on off on off. Does anybody know what this is???

Let me guess: It's a Mercedes-Benz!

Now if anyone could only guess the model and year, you might get some help.

Sorry about that. Its a 1979 300SD Mercedes Benz

That will help a lot. Unfortunately, I've never dealt with one this old.

However, you can check the resistence of the circuit. You have the loop-style, series plugs, right? If so, disconnect the relay plug(s) and check the resistance from the "fed" plug to ground. By "fed" plug, I mean the one furthest from the grounded plug. I don't know what resistance you should read, but it shouldn't be either exactly zero or open. Post that here, and you'll give people more information.

Use the manual link in my signature and browse through the W123 section for a 1979 300D. There should be something in there that will cross over to a SD as far as the glowplug circuit.

The flashing is kind of a rudimentary "check glow system" feature.

You most certainly have one bad glow plug. On that system, if one goes bad, there is no power to any of them and, presumably, it's difficult to start.

my 79 SD has the pencil type plugs. Do your glow plugs have individual wires for each plug??

__________________
'80 300SD - 315,xxx miles,
'79 300SD - 199,xxx miles

That right? Didn't know the 79 had the newer plugs..........

If so, then the one plug won't cause the others to go out. You can do a resistance check of the plugs by pulling the connector at the glow plug relay. Check resistance to ground on the lowest scale on the meter.

You're looking for .6-1.2 ohms or so. One of them is probably open (infinite resistance).

The plugs are the 12mm type not 18mm.

Did you run the resistance check on them?

One plug goes bad the light blinks. 2 plugs go bad the light does not go on. Change all the plugs you will be happy you did. Been there to many times in 35 yrs of 123"s RAY M The car will run on 3 glow plugs only but thats not good, on a 5 cylinder.

I did a resistance check today. four of them were between 1.4-1.6. The other one was open.

the same exact thing was happening to my car for a wile and it was while I was driving it, it was preaty hard to start but my engine is gone now, at least i think