Glow Plug / Heating Light Advice Please

Hi Guys - need to draw on your knowledge again please

1994 Defender 300 TDi

Yellow glow olug warming light stopped working today. Still starts even at -8 which is impressive!

Have checked (and replaced) the instrument bulb and ensured dashboard connectors all secured.

Checked both 60 amp fuses in the engine bay.

Two questions:

1) Is the glow plug relay the one in the engine bay on the bulkhead? Not checked that yet - need my assistant to come home!

2) Can I check the glow plugs are getting power without taking one out - nervous it might snap off in the cylinder head! Presumably a multi meter from the glow plug wire to earth would confirm?

Thanks - and sorry if basic - just new to this

Anything else I should be checking?

I have the same vehicle as you and didn't realise there was a glow plug light (will go and check in a bit ).

I cant answer your first question but for the second question - yes.

You can check that power is getting to the glow plugs by measuring the voltage on the feed wire. But for any vehicle, dont necessarily expect the light on the dash to be on at exactly the same time as the glow plugs are on. They are rarely connected together directly.

The glow plug lamp on the dash is there to remind you to wait for the glow plugs to warm the cylinders before starting the engine. But its normal (expecially in more modern vehicles) that the glow plugs themselves will stay on a lot longer while the engine is running and warming up. On very cold days that may even be until you've pulled away and put some load on the engine.

I'm not sure exactly what the deal is in our year defenders because I haven't tested it.

Thanks for replying

Yellow light was working before today.

Read a number of threads that comment that the engines start pretty well without the glow plug relay connected.

Think next step is to check relay operation and power to glow plugs.

If power is getting through I'll just count to 5 before starting! If not, relay swap out beckons

Do oyu know if the relay is in the engine compartment - have read about fuses behind steering wheel and relay and fuses under drivers seat - not finding anything in those locations in my one

Yeah mine start immediately in all weathers. Put the key in and turn and its running. I've never given even a second to warm it.

Just looked in the Haynes manual schematic. It says there's a cold start indicator (although that's probably the one you're talking about, even if Haynes use different terminology). Also the glow plug relay doesn't look like a normal relay. It has more connections to it and is marked glow plug timer.

I'm afraid I dont know where it physically is. Hopefully someone will be on here soon that knows.

Definitely do the voltmeter on the plugs before forking out for a replacement relay/module. Chances are they'll be a bad earth or frayed wire or similar that can be sorted without cost.

I know mine has some dodgy connections there somewhere. The cigar lighter stopped working, and my dash illumination works only on alternate days it seems, but for some reason if its having a day off, it works again if I put the wipers on (but not on intermittent). V.strange. Just haven't got round to having a looking at it yet.

Station House said:

Hi Guys - need to draw on your knowledge again please

1994 Defender 300 TDi

Yellow glow olug warming light stopped working today. Still starts even at -8 which is impressive!

Have checked (and replaced) the instrument bulb and ensured dashboard connectors all secured.

Checked both 60 amp fuses in the engine bay. Check them again. They usually crack rather than blow. This can often be almost invisible to the naked eye. If needs be try replacing or switching the 60 amp fuses over to double check.

Two questions:

1) Is the glow plug relay the one in the engine bay on the bulkhead? Not checked that yet - need my assistant to come home! Yes. You should be able to hear/feel the relay clicking in and out. The brown wire is the live feed. Check it is getting 12v.

2) Can I check the glow plugs are getting power without taking one out - nervous it might snap off in the cylinder head! Presumably a multi meter from the glow plug wire to earth would confirm? Yes. use a multi meter or power probe attached to the top of the glow plug and see if it comes live with the ignition on.

Thanks - and sorry if basic - just new to this

Anything else I should be checking? Yes. If the wiring is the same colour on the defender as it is on the discovery, check the yellow wire on the back of the ignition switch is going live.

Click to expand...

Answers in red

Ratty/Mundungus - many thanks

Voltmeter standing by!

Well, my willing (ok, conscripted helper) got back - no clicking timer relay and no voltage at the glow plugs.

Pulled the connector off the timer relay and confirmed permanent 12v feed and switched 12v feed from the ignition switch.

Assumed therefore a faulty relay - replaced the connector and.............the orange warming light is back to working!

A good old coroded connection I suspect - have liberally coated with silicon spray and will keep everything crossed that that's it cured.

Somehow suspect I'll be turning the ignition key with suspense for a while yet!

Thanks again for the advice.

Station House said:

Well, my willing (ok, conscripted helper) got back - no clicking timer relay and no voltage at the glow plugs.

Pulled the connector off the timer relay and confirmed permanent 12v feed and switched 12v feed from the ignition switch.

Assumed therefore a faulty relay - replaced the connector and.............the orange warming light is back to working!

A good old coroded connection I suspect - have liberally coated with silicon spray and will keep everything crossed that that's it cured.

Somehow suspect I'll be turning the ignition key with suspense for a while yet!

Thanks again for the advice.

Click to expand...

A nice cheap fix.

Yep - a refreshing change having wanted to keep my fingers warm this week and paid for the timing belt to be changed!

Thanks again