24 Volt mystery

So, I have just purchased a 1985 110. 2.5 NA diesel.
Its ex Singapore military and has the 24v wiring.
Everything in the vehicle is 24V. 2 batteries in series and huge alternator...
The vehicle wasn't running when I got it
I went through everything and found that all the glow plugs were dead.
Installed new glow plugs and it fired up straight away after a 15 sec glow.
Went to start it the next day and it wouldnt go. Pulled the glow plugs out and found no4. and no.2 had melted tips and no.3 and no.1 while not melted are very dead.
System has a relay on the bulkhead. That seems to check out ok. Comes on when the key is in the glow position and goes off when released. The feed to the plugs from the relay is 24V according to the meter.
Next to the relay is a small ballast resistor with 1 very thin wire attached to each end . Not sure why its there or what its supposed to do.
The glow plugs are wired in series.
The new glow plugs have 11V stamped on them. Checked the old plugs that came with the car and they are also 11V. Can't blame the parts guy for this one!
My question then is...Should I have 24V glow plugs? OR is 11V correct and something else is going on?
If I do need 24V pugs where can I find some that do not have an insane price tag attached to them?
I'm hoping someone here can shed some light on this as nobody in NZ can. The mention of 24V makes parts people go crosseyed here.

Cheers

I would rewire the glow plug circuit to make it supply 12v. There is no reason why your plugs should be 24v. I think some previous owner has bodged the wiring.

Col

In my opinion, they should be fine if they truly are in series, are you sure?

Colthebrummie said:

I would rewire the glow plug circuit to make it supply 12v. There is no reason why your plugs should be 24v. I think some previous owner has bodged the wiring.

Col

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Yeah I have thought about doing that and its also very likely that the wiring is bodged. It just seems odd to me that a 24v relay is feeding 24 volts to a 11v glow plug. How does that even happen?
Unless something is missing....

kermit_rr said:

In my opinion, they should be fine if they truly are in series, are you sure?

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Definately in series and definately all fried. Are you saying that 11v plugs are the correct ones and that they should be able to handle the 24v feed?
Cheers

2 12v devices connected in series, ie daisychained negative of one connected to the positive of the next, then you'll need 24v to power them

Any chance of a picture of the glow plug wiring ?
I think Glow plugs are all supplied by the feed loops (i.e. in parallel) so they will all get whatever voltage is applied via the relay unless you have glow plugs that have 2 connections ?, the grounding takes place via the threads into the head.

As @Colthebrummie said I would rewire the relay to control only 12v to the glow plugs, you can leave it controlled by the 24vs but get the relay output to switch 12v

marksman said:

As @Colthebrummie said I would rewire the relay to control only 12v to the glow plugs, you can leave it controlled by the 24vs but get the relay output to switch 12v

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I think im going to do just that. I'll wire it for paralell which is a better setup anyway and just get some new 11v plugs.
Thanks to all for your help

Can you get hold of an official wiring diagram for your vehicle and then rewire it accordingly? The plugs should be in parallel on a 110 so something needs to change. Can you take a glow plug to a diesel truck specialist and see if you can get hold of a set of 24v plugs?

Did you every get this sorted?. I literally just bought an ex singapore military 110 ambulance and it has the same relay/ resistor setup. Only I have another issue when the relay is connected to ground and not positive and no voltage at glow plugs. Wondering what solution you came up with before I go tracing the cable and connect it to 24v which sounds like it will just chew through glow plugs(which is why it was probably disconnected)

dandwyerirl said:

Did you every get this sorted?. I literally just bought an ex singapore military 110 ambulance and it has the same relay/ resistor setup. Only I have another issue when the relay is connected to ground and not positive and no voltage at glow plugs. Wondering what solution you came up with before I go tracing the cable and connect it to 24v which sounds like it will just chew through glow plugs(which is why it was probably disconnected)

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I never got to the bottom of the mystery.... I still dont know which plugs it should have.
The cost of 24V plugs is outrageous here in NZ so I followed the advice above and wired the relay for 12V and went with 12V plugs.
The resistor output is 12V and that controls the relay. (24V from the key switch into the resistor then 12V out to the relay)
This makes the relay and glow plugs an all 12V affair
That worked fine.
The wiring in my 110 is a complete mess so I'm ripping it all out along with the 2.5NA and going 300Tdi and all 12V.

What kind of resistor did you use? And what kind of amp rating?. It was my understanding that the glow plugs pulled a lot of amps.

dandwyerirl said:

What kind of resistor did you use? And what kind of amp rating?. It was my understanding that the glow plugs pulled a lot of amps.

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You can use the resistor thats already there
It doesnt need to be big as its only carrying the signal voltage from the key to activate the relay.
The Singapore trucks have two 12V batteries wired in series to give 24V. (The + post of battery 1 is connected to - post of battery 2)
In my truck the batteries are under the passenger seat and battery 1 is the one nearest the front of the vehicle.
If this is the case with your vehicle, do the following...
You can check with your volt meter to find out which one is battery 1. You are looking for 12V. If you see 24V you are attached to battery 2
Now, look at the yellow wire which runs from the relay to the glow plugs
Find yourself some similar thickness wire and attach it to the + of battery 1
Then run it under the floor and up the bulkhead to the relay
Unplug the original power wire from the input pin on the relay (I think its no.30)
Take your new power wire and attach it to the input pin on the relay
You relay is now all 12V.
Check it with your meter by turning the key to the glow position and measuring the voltage at the plugs
Enjoy the awesome noise and vibration of the 2.5 NA

Man you have literally saved me an insane amount of time! Ha. Yeah the 2.5NA is not a refined beast but it is simple and really difficult to kill. One thing I will say is the Singapore military had one hell of an interesting combination/setup on their vehicles