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Disco 1 300TDI glow plug relay wiring


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97 Disco, 300TDI LHD.

Some help needed please to understand what I should be seeing.

No power getting to the wire on the glow plugs (0 volts) .  Relay clicks on and off, light on the dash goes on and off.

Relay/timer situated right behind the fuse box near the battery. It has 4 smaller black wires and 2 large , a Brown/Orange (N/O) and a Black Yellow (B/Y).

I guess the B/Y is the feed to the plugs.  The N/O has no power to it (0 volts), even with the key turned to the position where the plugs should operate. I am assuming this is the problem.

Am I right that the N/O should be live?  Any idea where it goes to?  It disappears into a loom, and it's a hard plastic covered example.  Is there a fuse somewhere?

Any help or ideas appreciated.


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12 hours ago, Alsace_rangie said:

Am I right that the N/O should be live?  Any idea where it goes to? 

Yes it should be live, it goes to a fusible link described as being "P119 Fusible link -  RH front of engine compartment behind battery"  there is no clear view of it in the manual, it might be wrapped and not visible, better route a new wire to the relay's pin with a 60A inline fuse holder from the battery positive terminal



300tdi glow plug circuit.jpg

Edited by sierrafery
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Is the NO line always live, i.e. not switched by the ignition key?

But you are right, i can't see any in-line fuse.  The wire goes into a loom enclosed in hard plastic flexible trunking, then branches.  I one of the branches does head to the adjacent fuse box, but no easy way to trace the wire route without making a mess.

So as suggested, take a live feed with 60A fuse.  May try one of the waterproof trip/reset ones you can get.  About the same price as a conventional waterproof inline fuse!

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You can work with a inline fuse holder which has wires too like this https://www.ebay.co.uk/itm/Maxi-Blade-Fuse-holder-splash-proof-waterproof-holder-free-fuse-8awg/281667851189?hash=item4194b653b5:m:mw2tqx9HUWfJF8L7Np5piqQ&var=580673049497 , the fuse is higher ampage than the wire gauge cos it's supposed to blow on a short to ground but for 300tdi glow plugs 40A fuse is enough

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OK, assumed the 60A was a "last resort" level.  Off to sort out some wire (5.7 or 6mm2) and an inline fuse .

I'll probably expose as much of the existing NO wire (attached to the connector) as I can and cut/join that to the new fuse.  Of course I'll put an insulated connector on the bit left sticking out of the harness/loom.  It's dead right now but might spontaneously fix itself some day 🔥

By the time I get the bits and find time in the next few days, the weather will be warmer and I won't need the plugs, but it'll be ready for next winter 🙂


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