Glow plugs, Ballast resistor

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Fatrover

Fatrover

Well-Known Member
Posts
921
Location
Argyll, Scotland
1976 Series 3 Diesel, Series connected glow plugs.

No glow plug light the other morning and plugs not heating so I replaced them with a new set of pigtails and left them wired in series. I also replaced the wiring.

Still no glow plug light but, 12 V feed into the first plug from the ballast resistor. Thereafter no voltage at the subsequent plugs.

The first time I tried to start it after doing the replacement, the glow plug light came on although in the second heat, back to nothing.

Can anyone tell me if the feed from the ballast resistor should be 12v into plug 1? If so am I right in thinking that the new plug 1 might already be shagged?

Cheers,
J
 
I’ve just checked the old plugs by connecting them across the battery, individually, and they’re all knackered. Makes me wonder if they’ve all been fried as have the new ones . Ballast resistor knackered?
 
The ballast resistor should lower the voltage from 12v to a lot less maybe 6-7 volts , the 6v heater plug bulb only needs an earth and that 6v to glow , each subsequent plug gets a lower voltage then the one near front needs to be earthed
They need to be wired carefully so you don’t short them out using the proper insulating washers as in pic

Ballast resistor is just a wire so unless there is a break in it should be ok , the terminal posts I recall are insulated from earth too.

IMG_3696.png
 
Thanks Steve, that’s v useful and looks exactly like what I’ve done!
Here’s a pic of the new plugs I got, I’ve taken them out this morning and tested them across a battery and none heat up. I think they’ve been fried as I measured 12v going into the one nearest the bulkhead yesterday and the voltage remained the same across the other plugs and out the other end.
IMG_2297.jpeg
 
Last edited:
Aye it’s either or at the minute, both have benefits right enough.
Original plan was to just replace the series as they’ve lasted fine since 1976.
Will need to get the resistor out an see if it’s bolloxed, might be the source of all this
 
Here’s the ballast resistor, the new plugs went in exactly as per the old series wiring. Power to the first plug is via the red cable will remove the whole thing tomorrow and get a look. I measured 12V coming out the red wire into the first plug yesterday, got the Mrs to turn the key and stuck the multimeter on the end of the red lead as it connects to the first plug, only for a few seconds but was deffo 12v
IMG_2298.jpeg
 
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the pic looks ok apart from the wire colours the two thin ones go to the bulb, and a fat Brown/red supplies the 12v on yours it looks black
when you turn key to heat i would expect to see 12v on the black dropping to 6-7volts on the red , you can see on diagram below if there is a break in wiring or any plug between ignition switch and last plug there will be no earth so the 6v bulb will not come on then
perhaps might see a bit more tomorrow after closer look
the resistance of the plugs looks like about 0.1 ohm if you want to test them , the ballast resistor should be similar too


1734722828029.png
 
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