Glow plug electrics


i have recently put a 2.8td daihatsu fourtrak engine into a land Rover. I didnt have the daihatsu wiring loom when i did the conversion and as a result i fried the glow plugs because i put 12 volts to them when their only 7. Im using a daihatsu glow plug relay but what do i need/do to get the voltage down? can anyone help?
Thanks matt

Glow plugs

Hi Matt,

How do you know the Fourtrak only sends 7 volts to the glow plugs? As far as i know the relay just sends battery voltage to the relay and then to the plugs, (i'll have to have a look in the morning and check with a volt meter). How were you switching on the glow plugs on your Landy, because they only need about 2 seconds to heat up enough to start the engine.


glow plug voltage

I have seen a posting on this site recently re the heater plug voltage, do a search.

Edward (ews) '92 Fourtrak 2.8 TDX

Do a search

.... for 'glow plug' and for 'heater plug'

Lots of info here (I wrote some of it and, for my sins, call 'em heater plugs)

Without the timer unit, temperature sensor and current sensor that the Daihatsu uses, the plugs will be fried by 12V (the timer cycles the plugs on and off to keep the average voltage sortof about 7V).

The best way to do the job is like the arrangement on my Series 2A diesel landrover (long since gone, albeit VERY slowly). This had a chunky series resistance in line with the glow plugs to drop the voltage. The timing was done by the driver turning the ignition switch to a special 'glow' position, counting to 5, or 10 (cold day), or 20 (extreme brass monkeys), then attempting to start.

I've identified a resistor which should do the job. Before you get too excited, I happen to have one in my electronics box which I use for something else. I'll graft it onto my 4trak by way of experiment and report back in a couple of days.

I'm putting in an order to CPC next week, and can send you one if things work out OK (send me a PM)

PS You might get the homepage
You will have to search on that page for RE03525

.... 8.3 Volts OK ?

Checked it out this morning after a long run last night (battery was still at 12.9V).

OK, this is still a bit of an overload, but the voltage will drop if the battery is feeling a bit out of sorts.

The dissipation in the resistor is 160 Watts, which is cooking it, but for the duration of the glow time should be OK. To be sure that the resistor doesn't expire prematurely, it should be heatsunk .... no you don't need to buy one of those finny chunks of ally. All that will be required is a 6" by 6" chunk of flat aluminium sheet 4 to 6 mm thick. Even with this, if the heater plugs are left on continuously the resistor and ally plate will reach something like 150 degrees C after, say, 30 minutes.

wiring info

First you need to drive the relay coil.

Using 0.5 square millimetre wire you will have to connect from the 'ignition' position on the main switch to an auxiliary 'heater plug' switch that you will have to instal on the dash. The heater plug switch should be a push button or polarised type that will switch itself off when you take your finger off it.

The other end of the switch needs to go to the relay coil and the other end of the relay coil goes to earth.

If I remember OK, the Daihatsu glow plug relay has two 'nut and bolt' connections for the high current circuit. From the battery positive terminal, run at least a 2.5 (preferably 4) square millimetre wire, via two 30 Amp automotive fuses wired in parallel, to one of the nut and bolt connections on the relay.

Using the same wire, connect the other relay 'nut and bolt' connection to the 0R1 resistor mounted on the aluminium heatsink as described in my previous note. You will have to find a place for this somewhere in the engine compartment. The resistor connections are designed to be soldered. As a precaution against short circuits and as extra support for the soldered connections, I use heatshrink sleeve over the resistor ends.

Finally the other end of the resistor is connected to the glow plugs, again using the heavy cable. I am presuming that you have the bar of metal that comes with the daihatsu engine and connects 3 glow plugs together and the wiggly resistor element that connects the fourth.

Sorry to teach gran to suck eggs, but the way this lot works is that when the electrics are on, current is available to drive the relay coil via your new 'glow plug' switch. When you want to start, turn on the 'ignition' as normal, push the new glow plug switch for 10 or so seconds (more if it's cold) and then turn the key to start the engine.