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Hi I am new here and it looks as if there a lot of brains here. I wish I had one! I just installed new arnley glow plugs in my 1985 s 15 gmc. Only one of the old glow plugs tested good for continuity. It is still slow to start some what. Some one had fastened a wire to the last glowplug at the firewall and it seemed to go to the ignition switch, the factory wire color the new wire was attached to was green. I put new connectors on the battery and the wire and terminals are good. I wonder what I need to do next?? With a volt meter what voltage should I be getting at the glow plug when the ignition key is on and the wait dash mounted WAIT cycle is underway?? Thanks for your help!!!!

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Excuse me while I tinker with my diesel s15.

It really depends on the truck...luv diesels have a drop down resistor that pulls 12 volts to six volts to run the luv glow plugs.....with my luv...I have taken the drop down resistor off and am using 12 glow plugs.....You shouldl get either 6 or 12 volts at the wire during the cycle for the plugs to heat up......Hope this helps

I just went through the glow plugs on my Luv.

The Isuszu 2.2L diesel uses 6V glow plugs jury-rigged to run at 12V until the temp reached some temperature (400 degrees, I think.), and then switch to 6V via a pair of relays until the plugs reach a higher temp (~900 degrees?).

All this is controlled by your glow plug control box which takes readings off your thermostat housing and off the glow plug power rail.

If someone has bypassed the control box and voltage divider, they could hook a relay that is turned on by the wait light circuit, to supply either 6V or 12V to the plugs. When the lamp turns off, the glow plugs are also turned off.

That said, you might see either 6 or 12V at the plugs. 6V would be the safer voltage to run. 12V might provide too much current and, although the plugs would work faster, they might burn out sooner.

A good alternative to jury-rigging might be to install a thermistor in series between the relay-controlled battery voltage and the plugs. As the thermistor heats up (with current flowing through it), it will automatically increase its resistance and limit the current to (voltage across) the plugs.

Hope this helps.

The 12 volt glow plugs also work quicker and also are more efficient as well as will last longer than a 6 volt glowplug and also are less expensive and easier to find.....Have had mine on 12 volt for almost a year now with no problems...........If the luv has a dropdown resistor they will run six volt all the time unless aftermarket parts have been added if i am not mistaken

I have been running the stock glow plugs in my Sonoma for 2 years without the control box, and one relay with a manual push button to activate the relay. A 3 second count works for them, and they last that way.
Oddly, my plugs are marked 5 volts on them, not 6.

Where did you find 12v plugs to fit the Isuzu?

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Bona Fide diesel fanatic.
1994 Chev S10 Ext Cab Isuzu Diesel 5spd
Kubota B6100 HST diesel

Thanks for all the input fellows!! I checked my ney glow plugs this afternoon and it seems I am getting only 2 or 3 volts to them. I think I am going to by pass all the gmc factory electronics and just use a push button switch and count to 3. I wonder if its ok to just reduce the 12 volts to 6 volts and attach one wire to the rear glow plug and send current to all 4 plugs via buss bar or should I fab up a harness and power each one indivdualy?? Thanks again!!

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Excuse me while I tinker with my diesel s15.

Six of one, half dozen of the other as long as you're supplying the same voltage to all of them.

2-3V would indicate a resistive path somewhere where there's not supposed to be one. You may have a corroded battery terminal, or one of your connections to/from the controller box may be dirty. Either that, or your battery is weak, which would be obvious when you tried to crank the motor.

I bought them in a parts warehouse before i left oregon...they work though.....heat very quick.....I would check all connections and the relays...let us know how it goes

Thanks for your help fellas. As soon as I get this little baby diong right on diesel I am gonna go the veggie + diesel conversion route. Pee on the big oil companys if you get my drift. I want to get in good with a good local resturant that uses nice canola cooking oil before the rest of these local rednecks figure all this out and gobble up all of the waste oil. Big oil gurus are saying $3 gas this summer. Prepare now before the big dogs lower the boom on us. Best wishes to all , Rob

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Excuse me while I tinker with my diesel s15.