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Engine compartment fuse box & glow plugs

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Having replaced the glow plugs, ignition barrel and glow plug relay the glow plugs are still not receiving 12v

This is what I know :-

The dashboard lights (incl the glow plug one) all work perfectly

There is continuity between the glow plugs and the black/yellow wire on the relay

The yellow/black wire from the relay clearly works as that feeds the dash instrument pack

The black wire from the relay has a good earth

The white/red wire from relay to ignition Position II to crank the engine is working fine as the engine turns over

The white wire from relay to fuse 17 and Position I on ignition is working OK as dash glow plug light working ok

I understand looking at the 300tdi wiring diag that one of 60 Amp fuses in the engine compartment fusebox feeds the glow plug relay on the brown wire

SO by a process of elimination it must be this 60 Amp fuse that has blown - does this fuse feed any other cicruit ?

By writing this I think I have convinced myself that this is the source of the problem - unless you can tell me otherwise!


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Was surprisingly straight forward. Used those nice chaps at vwp to make up the 2m of 40mm2 starter cable with an 8 mm terminal end which went straight on the starter earth. Fed the cable along chassis and up into battery box. Cut off the 20 cm of cable which was not needed and then use another 8 mm terminal end and a friends crimping tool and job done. Secure new cable appropriately along way with cable ties etc.

Checked all other earths while I was about it and now the starter motor is alot stronger and faster

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  • 5 years later...

I'm trying to figure out the operations of the glow plug timer unit for my project car. The original engine came out of a disco 1 300tdi that is now long gone.

I'm pretty sure that when I energise the relay it clicks on for about 5 seconds then clicks off. Also pretty sure that glow plugs do fire up for that period.

So that's the normal relay contacts dealt with and the timer function.

Now I'm left with a white/green cable and a black/yellow cable. According to the diagram earlier in this thread the White/green is spliced into the same circuit as the starter solenoid so is presumably an input to the glow plug relay. The B/Y wire goes to the warning light on the dash. In my case a 5w side light bulb.

I'd have thought energising the W/G wire (cranking) would then shut off the B/Y output or it would also shut off after the timer completed.

My does not do this. If I connect the B/Y wire through the bulb to earth then the bulb is perminantly on when the relay is energised. If I connect it back to the W/G ( as per diagram above) it never comes on

Anyone any insight into what I have wrong?

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