Checking heater plugs in place

My heater plugs have died (seemingly suddenly?). I took them out and tested them and 3 out of 4 failed to even become luke warm.

So I'm going to replace them, but this raises two questions for me.
Not sure from what I've read whether the orange "Cold Start" light should come on when the glow plugs are working or when they reach temperature. Which is it? (never seen it come on at all even after 20 seconds on heaters on a warm day :S)
Secondly, how do I tell if I have a wiring fault that prevents them from working at all? Any way to test them in place? (For all I know they've never worked since I got the landy).

hi there you could always connect a test light to heater plugs in situ one end earthed and the other on plug and get someone to give the heat,if it lights up job done if not it could be the resistor hope this helps.

Wh at model is it, I.e is it one with the plugs in series or parallel?
From memory the cold start light is meant to be out then glow brightly as the plug resistance goes up (Maybe other way round).

Just reread your post. If you tested individually on a battery and they didn't get hot then they are duff.

as said above, depends on which you have installed.
if its a genuine series 1.25 diesel, you should have series plugs. these should look like a coil of wire on the end of the plug when you remove it, and the connections for wiring have an insulator between them. if one plug fails, non of them will work. the last plug is wired to the block.
likewise, they have a ballast resistor in the circuit, usually bolted to the bulkhead. its a plate of steel with a wire coil behind it. the glow plug light on the dash is connected across this and should start off dim increasing in brightness as the pulgs warm up. (its the voltage drop across it that causes it to glow). if this ballast resistor fails, it will also render the glow plugs ineffective. the orange light will not work in either case.
quick test, to see if the orange light has failed is to wipe a finger of oily goo usually found in the engine bay somewhere (or even off the dipstick) onto the ballast coil. with an operating set of plugs, the ballast will get hot enough to visually see the oil smoking as it burns off.

second type of plugs is the parallel type, retrofitted from the later engines. these just require a 12volt feed to work, and the orange light is connected from glow plug to earth. it will be either on or off, no glowing and getting brighter. there is no earth on the last plug. if one plug fails, it will not affect the remaining plugs, but make it harder to start the engine. testing is by disconnecting the wiring and testing resistnce to earth individually, or removing and checking for actual operation with a decent 12volt battery.
test circuit with either a multimeter or test lamp.

both types should glow red hot in about 4-5 seconds, tho the latter are better.

Hi, - im really glad i read this thread. I've had problems with starting for a while and suspected something wrong with my heaters. I've had them out and checked individually and they all glow red. - noticed that plugs have different pt numbers on them (would this make a difference?) - 12v is there at the plugs.
Orange light glows brightly at start -and stays that way. Any clues?

Mugsey said:

Hi, - im really glad i read this thread. I've had problems with starting for a while and suspected something wrong with my heaters. I've had them out and checked individually and they all glow red. - noticed that plugs have different pt numbers on them (would this make a difference?) - 12v is there at the plugs.
Orange light glows brightly at start -and stays that way. Any clues?

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what engine year etc later engines use std style glow plugs but others use 6v plugs with coil on the end ,engines in series are poor starting in cold poor compression is usual cause a god bit of heat is needed to overcome that

Series 3 2.25 -1976 they're in series i.e. last plug attached to block