TD5 glow plug fuse goes bang

While chasing out another problem I found that my glow plug fuse had blown out. Hasn't been a problem so far but I'm planning on taking it somwhere pretty cold next year so I though I'd better get it fixed. I got a new fuse but I was a bit lazy and didn't even disonnect the battery (ignition wasn't on). As soon as it touched the contacts the fuse blew immediately. I did a bit of googling and thought it might be a stuck relay so I opened it up hoping to find a charred mess but it was just a pretty healthy looking copper coil thing. I'd just change them both out again but it takes about three weeks for me to get these parts delivered.

I'm terrible with electrical stuff. Might it still be the relay? Where else should I be looking? Am I right in thinking the problem must be between the fuse and the battery?

It could be a short anywhere in the circuit after the fuse.

But the really must be faulty as well right? It shouldn’t be drawing current with the ignition off if the relay isn’t stuck closed.

Does it blow the fuse/draw a large current when measured with a multimeter even with the relay disconnected?
If it does with the relay removed then you know there is a short somewhere in the wiring between the fuse and the relay. If it doesn't then you know the problem is relay onwards.
Again with a multi meter or even some wire and bulb you will be able to test the relay for continuity to see if it is stuck closed or not.

Twinnie said:

<snip> I'd just change them both out again but it takes about three weeks for me to get these parts delivered.

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Why does it take 3 weeks to get stuff delivered to London ?

dag019 said:

Does it blow the fuse/draw a large current when measured with a multimeter even with the relay disconnected?
If it does with the relay removed then you know there is a short somewhere in the wiring between the fuse and the relay. If it doesn't then you know the problem is relay onwards.
Again with a multi meter or even some wire and bulb you will be able to test the relay for continuity to see if it is stuck closed or not.

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Thanks, I’ll take a look at that when I get home.

miktdish said:

Why does it take 3 weeks to get stuff delivered to London ?

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I haven’t updated my details. I live in Africa now.

are you referring to fuse link 1 blowing as this supplies several other items

Is there anything else not working that may be the cause of the problem, like a seized blower fan motor overloading the circuit, what is the other problem you were working on.

The other problem I was working on was that the horn isn’t working.

I tested pulling the relay. When it’s in I get about 14v across the fuse, when it’s out it goes down to 0.3v. I would’ve expected it to go down to 0v. I wanted to test the relay but there’s four connectors on the bottom and I don’t know which ones to test.

Thanks. So I’m checking between brown and yellow. I’ll do it tonight.

brown feed ,yellow/black to glow plugs .if the relay is removed and the fuse does not blow check each glow plug and inter wiring ,if fuse blows with relay out then problem not glow plugs and if it does not blow any of the fuses shown in the first diagram then the fault is between fuse box and glow plug relay would check you have not pushed any of the connection tabs out of the relay holder and contacting the body work

Thanks, been looking back at that diagram and I think I have a relay that’s stuck closed and a bad earth between the fuse box and the relay. I guess I’ve got a fun Friday night ahead of me.

mystery said:

View attachment 284172

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Sorry, I only just noticed this message. It does look different to the other diagram, does it just have more detail then? It’s the 100amp fuse under the drivers seat, it’s labelled as being for the glow plugs in the little diagram under the lid. First thing I’m gonna do when I get home is test the relay and see if it’s stuck closed. That’ll be one thing fixed and then there’s something else that’s causing the fuse to get overloaded, probably and earth. I’ll just have to trace that out.

I haven’t got any way of checking the amps until tomorrow but I took the relay out and tested it. It was definitely stuck open so I gave it a tactical whack against the seat box and it fixed it. I opened it up and gave it a good blast with contact cleaner and it seemed to be nicely freed up.
I put it back in and turned the ignition on and measured 12v across the fuse for a few seconds but then it dropped off again. Has the ECU detected there’s a problem and turned it off?

the glow plug relay is controlled by the engine control unit and called when the engine coolant temperature sensor requires it .there will be 12volt either side of the relay coil
and the ECU grounds one side to allow the relay to activate. probably only flashes the relay to illuminate the glow plug warning lamp if coolant temperature is optimum
It is unwise to use relays that have welded on as the coating on the contacts is damaged and it will weld again .
is the fuse link blowing with the relay removed as previously requested as this would eliminate the glow plugs and it circuit

mystery said:

the glow plug relay is controlled by the engine control unit and called when the engine coolant temperature sensor requires it .there will be 12volt either side of the relay coil
and the ECU grounds one side to allow the relay to activate. probably only flashes the relay to illuminate the glow plug warning lamp if coolant temperature is optimum
It is unwise to use relays that have welded on as the coating on the contacts is damaged and it will weld again .
is the fuse link blowing with the relay removed as previously requested as this would eliminate the glow plugs and it circuit View attachment 284253

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Thanks for the reply, sorry I missed it. I’m still waiting for my next fuse to arrive so I can’t test it right now. All I can say is that when the ignition is off or when I’m the relay is pulled I’m measuring about 0.1 volts across the fuse. When it’s on I measure about 16 volts. I can find a bulb to test it with but how do I know whether or not it’s over 100A?

AS temp solution https://www.ebay.co.uk/itm/39318185...4a56b49fca8032477213a6b94&pid=101195&rk=1&rkt

Thanks Mystery, I didn’t spot that but it I’ll do that test before I put my new fuselink in. I’m updating this as I think I’ve found the problem, I know I mentioned the horn but I hadn’t actually clocked that the 100amp fuselink was part of the circuit. I’d changed the cylinder head a few months ago I’d put one of the glow plug connectors back in and it looks like it has broken when I did that and was touching the head. I’ve replaced that now. Unfortunately right after doing this my multimeter broke when I left it in the sun. I’ll see if I can dig out another one and run your test before I connect the new fuse. Thanks.