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Glow plug wiring - 19J off ignition switch - zero volts. Please can someone help....

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Hi all, time for another perplexing query that I hope someone can help me with please.....

1986 110 CSW with a 19j unit onboard.  Issue is with the glow plug Brown / Red cable from the ignition switch to the glow plug loom.  I should be seeing ( I think) about 9 volts.  I get a reading of almost zero volts at position 1 and 2, zero on position zero but 8.9 volts when I spin the engine over.

The engine fires (eventually), all other circuits appear to be ok with dash lights etc.  all present.  just no volts at the plugs,

I've replaced the ignition switch (PRC2735) as that had to be the only possible answer - surely.....  All the wires are back to the original setting (2 for the glow wire etc.).  There are no relays, fuses etc. in line from the switch to the glow plugs. I get a reading of 90mv on position 1 and 2, zero on position zero at the ignition switch end.  What on earth !!!!!!!!

I've checked every fuse, relay and traced the glow plug wire from switch through bulk head to the plug - no breaks etc... zero resistance across the entire length of the cable so should be good....

I've looked at some past threads that all seem 200TDI related and relay based.

I'm missing something here or the Gods of Looms are punishing me for some unspeakable past offence...   any and all input hugely appreciated.  I simply cannot see a way through this...

Huge thanks,  some images in case they help.  Chubby.

Ignition switch - replacement PRC2735.jpg

Fuse box and glow plug cable.jpg

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I think you have a couple of issues here. 

1. You should be seeing more than 9v.are you getting just 9v at the battery terminals? 

2. You might have the ignition switch wired up incorrectly. 

Just connect the brown 12v wire up for now then with your multimeter see what terminal becomes live as you move the key to the different positions. Basically you should expect all terminals to be off with the key out. Then different ones become live with the key in the different positions... I have a post on this somewhere on my re wire thread. The brown/red wire should be connected to the terminal on the back of switch which becomes live as you hold the key in the pre-heat position. 

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This is what the back of my switch looks like on my 1988 110 with a 19J engine. Be careful though as I think @westernsays his switch for a 1989 110 (originally a 19J) is a bit different to mine. 1651098101_IgnitionSwitchwiring.thumb.png.4baf3398de96692bbae1297efc2c20a8.png

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What are you using to measure the voltages? I assume it must be some sort of multimeter?

You need to check the voltage methodically along the wiring, if need be all the way back to the battery. Something in the circuit is creating a high resistance.

Don't assume the switch is good just because it's new (especially if it came in a blue box).

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Thanks all - spent a few hours going over this all again, I hope the below will help shed some light....

I am 100% certain all wires are in their original positions on the replacement switch - I was very careful here. The glow plugs used to work prior to strip down of the truck.

I'm getting 14v at the battery - its only 4 months old.  I have even had the entire fuse box out, checked and replaced fuses, cleaned terminals etc....

Ignition switch positions and voltages measured...  not at all like the above...  I am now very lost 😞

I don't appear to have any feed at position 1, my wire here is white and black (fine wire).  There is a non used white / orange with a spade terminal in the loom - should this be on 1?

I have no volts at position 2 at all.  I thought this may be the switch hence changing it.

Any ideas please?  I've given up on the Haynes wiring diagrams too.....



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Right, using your terminology... 

Brown heavy is the permanent unfused supply to the switch from the positive bus on the starter motor. 

White red fine is all good as this goes to the starter relay to turn the engine over when the key is moved to the start position. It should be off in all other positions. 

Your white heavy needs to be live in positions 1, 2 and 3 as it supplies unfused power to circuits that are essential such as the stop solenoid on the fuel injection pump and some of the fuses for other stuff that are live with the ignition on. 

Your brown red heavy needs to be live in position 2 only as this is the glow plug feed. 

I understand white black to be the rear window heater but that sounds wrong. This terminal by my reckoning should be live with the key in position 1 only (ie engine running) for things like the radio and heater fan. In fact this wire could be to the radio if fitted..?


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Posted (edited)

Key positions:

0= Off

1= accessories on

2= IGN ON Normal running


White orange is switched accessories on position 1. Normally this feeds the radio and bizarrely the heater fan on my 300Tdi. So terminal 1.

White black according to Lucas codes should be distributor feed (and is on my series 3) but since you are diesel it could be the stop solenoid feed. So really needs to be on terminal 3, live when IGN on and CRANK.

In you table don't worry about mv readings, they are 0v for all intents and purposes. Don't measure any voltages when cranking the engine.

Pull off the white wire from the switch and re measure on the switch terminal, you should get battery voltage if the switch is ok. I suspect you are getting 9v and similarly 11v on the white red, as the vehicle circuits are loading the voltage. If you don't get battery voltage on these terminals with no wires attached, the switch is duff.

Brown red - if glow plugs and no timer relay fitted, should only be at 12v in key position 3.

Edited by simonb
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On the 19J position 1 should be the position where the circuits controlled by the ignition key come on such as heater, indicators, radio etc. Position 2 is the one where you manually hold it and count for however long you think is needed for how cold it is. Position 3 is start.

Glow plugs (brown/red wire) should be on in position 2 only on models with no heater plug relay.

Thinking about your sub 12v readings, is that because the engine is being cranked at the time you took the readings?

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Thanks chaps for your input and help.  I've remeasured everything, tried moving the white / orange etc.. and no changes.  Still no volts at position 1 on terminal 3 or 4 and no volts on terminal 2 at position 2 (glow plugs).

I think this means the switch if faulty - 4 days old and duff (and yes came in a blue box) - £23 wasted.....   I'll get another and try that and come back to you all.

Question - would there be value / benefit in fitting a relay based feed to the plugs like the 220tdi?  pricy as I need a new switch as well, but, is there any value in doing so?

Off to find a good PRC2735 now....

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Never assume just because a part is new that it will work particularly blue box parts. 

Yes you can upgrade to the relay like in the tdi fitted land rovers. There is a thread on this forum somewhere if you search for it. 

You will need a main feed from the positive bus, wire to the dash warning lamp, earth, supply to the glow plugs, white/red from the ignition switch and a white supply from the ignition switch IIRC. 


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The glow plug relay which is fitted to later engines contains a timer which continues to run the glow plugs for about 10 seconds after the engine has started. It's there to reduce cold start exhaust emissions, it has nothing to do with starting the engine. 

Keeping the original glow plug wiring would be simpler, and you would be very foolish IMO to consider changing the wiring without first getting the original wiring to work.

If you fit a relay you will also need a different ignition switch (PRC8230).

It does sound like you have a faulty switch but if you want to prove it, attach the negative lead of your multimeter to the chassis somewhere, and then, using a sharp pointed test probe, measure the voltage at first the battery +ve terminal and then at every accessible terminal or connection between the battery and the glow plugs. Measure the voltage both with the switch in position 1 (ignition on) and position 2 (glow plugs on). Somewhere you will find the difference between the two voltages is more than about 6 volts. The fault is between that point and the previous point where a measurement was taken and the voltages were within 2 - 3 V of one another.


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  • 3 weeks later...

OK - thanks first to @Mo Murphy for the genuine LR part.  now fitted and I've redone all my tests.

Oddly - no change...   the genuine part shows the same feed results as the original and the blue box part...   still no feed at terminal 2 (glow plugs) until I get to position 3 (cranking)...

I've tried to test every circuit over the last 48 hours...  to say I lost is an understatement...

I simply cannot understand how three switches all produce the same result, a result that is not what should be expected...

Anyone else with any ideas please?  I'm getting desperate now.......  The truck used to start on the button, with the glow plugs, pre strip down 5 years ago.


 Huge thanks in advance...


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I appreciate this shouldn't really matter but it's good to remove all sources of variables when faced with a problem. When you take your readings have you removed all wires to the switch apart from the solid brown wire on terminal 5 of the switch that is coming straight from the positive bus on the starter motor? 


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@monkie - Yes all cabling disconnected, only the positive feed on terminal 5.   I've chased the voltage from positive battery post to starter positive bus and an unbroken feed cable to the switch (t5). No loss of voltage etc.   I've also double checked all bulkhead fusing, no breaks.   The only possible area of breakdown / weakness may be the rear loom to bulkhead loom where the pins needed cleaning on reassembly but I cannot see any connection here to the glow plug circuit.  The switch is simply not doing what I / we expect.  And its the same for all three (the original unit, the blue box replacement and the new LR part).

I've even tried one of the units on the bench with a positive feed and home made "post" to turn it in case the barrel pillar in the lock mechanism was not turning correctly.  Same results as above.

@western Thanks for the lucas image.  I was looking at these earlier on a US forum set of posts.  Do I assume that ident 35288 could be a swap and details that there should be feed at terminal 2?    Its the same config of terminals as the three switches I now own 🙂

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"The truck used to start on the button, with the glow plugs, pre strip down 5 years ago"

Are you saying that the glow plugs have not worked since the strip down or have I misunderstood.


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Looking at the LUCAS diagram from Ralph, battery (brown wire) should be connected to terminal 1, which has a big end where it is riveted to the body and is at 11 o clock when the terminals are facing you. Your table suggests you have battery connected to terminal 5, which is at 5 o clock.

What happens if you move the battery connection to 11 o'clock and fill in a new table with voltages? If that then works then, 


red brown needs to go onto term 5, 5 o clock.

white black term 2, 2 o clock

white red, term 3, 9 o clock


The white blue which you mention is an ammeter, I would leave off for the moment, as it depends on where it is measuring amps, on how to connect it. They are never really a good idea as its more high powered cabling behind the dash, and a voltmeter tells you more. Get the switch wiring sorted and we can advise on the white blue later.


Edited by simonb
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@Chubby M does your switch look like the one on the diagram posted by Western? If so I think the above post must be right about terminal 1. My switch doesn't resemble the ones in the diagram so might be confusing you. 

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@Hawklord  Hi - yes the glow plugs were working previously - in so far as there was power at the brown / red lead, connected to the first glow plug on cyl 4.  Since strip and rebuild, oddly there is now no power at the ign switch.

@simonb Hi Simon, I'm still struggling with the LR part PRC2735, connected per diagram above from Monkey (5 July).  With this switch the only option for the Brown and Brown / Red leads are terminals 5 and 2 as these are the only two at 10mm spade ends.

I like the idea of the Lucas switch route, that though would be switch number four.... (3 PRC2735s) so far.

@monkie  Mine is currently the PRC2735, same as the image you shared.

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It is perplexing...  three potentially ok PRC2735 and the wiring matches as required, but still no power at term 2 for the glow plugs despite a constant and strong 12.6v at term 5 direct form the starter bus.

I've spent another four hours testing and looking for any fuses / relays that may be impacting - nothing...

Anyone want to buy a 110 project.......

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I very much doubt all the switches are duff.

Just because there are only 2 big terminals - doesn't mean you have the right feed on the right one. The switch internals aren't electrically symmetrical so if you have the feed on what is actually an output, the measurements on the terminals won't be correct - which does seem indeed to be the case - on all 3 switches. Hmmm....

The only common thing is they don't appear to be working, so you have nothing to loose from trying what I have suggested. Swap the feed on to terminal one (or what ever the other big terminal is labelled) and then see what happens. This is the only thing you haven't tried.

Report back and then we can go from there.

Monkie has already mentioned his switch may be different.

Can you post a terminal view of your genuine LR PRC2735 without any wires attached?


Edited by simonb
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