Below is an article I found online from Julian Burke that was very informative.------------------- OK folks, I see a need here to explain the starting system in the older Humvee 998 series and here is some scoop of the control boxes that are used in the older HUMVEE series. This should help some folks here. I have discussed this recurring problem with AMG, Wellman and KDS system engineers at length over the years and all agreed that this early control box is a piece of junk. The problem lies with the gov’t specs and it took Uncle Sam over 17 years to realize that this is getting to be an expensive ongoing problem that had to be fixed. Glow plugs are pretty much glow plugs whoever manufactures them. Wellman of Shelbyville, Ind. manufactured most or all of CUCV and Hummer series glow plugs for the gov’t. Their engineer there explained many things to me which was very useful in finding problems. You see, there are NOT really “12 volt” or “24 volt” glow plugs. A plug is rated at say 12 volts for 20 seconds to reach a temperature of about 1700 degrees. This plug can be left on for all day and will remain at 1700 degrees with NO harm to it or will “swell” out. This is what they’re supposed to do. 1700 degrees is a good temperature to get the engine to start. Now when you put 24 volts to the same plug, it will reach temperature in about 4 seconds which is how they do the “quick start” system. HOWEVER, if you leave 24 volts on it, IT WILL MELT or “swell” as most people say and will burn out after deformation. Now we get into the sorry controller that the gov’t specs called for. In the old system if your engine didn’t start, you would naturally turn the switch off and repeat the same process. Trouble here is that you would create a condition known as “STACKING’. You would be lighting the plugs again and if you repeated this several times, you would melt the plugs. The original controller box would NOT recognize this condition and would ruin the glow plugs! Then things went from bad to worse! The next generation controller had a propensity to catch the wiring harness ON FIRE or try to start the system by itself when no one was around. This box had the extra glow plug wiring harness that had to be installed. When Uncle Sam discovered this, all existing units were scrapped through the DRMO. Here is one instance where all of them should have been destroyed. (Like they normally do but noooo in this instance!) I have seen a few of these turn up on EBAY and either they don’t know or don’t care when selling them. Funny thing that when I would email the selling party about their control box they would ignore me or tell me to mind my own business. That’s all right though, I sent all prospective bidders the website so THEY would know. A few years back AMG lost about 6 brand new military only Humvees in the factory parking lot due to this condition. One spontaneously caught on fire and damaged/destroyed others around it. They never really said much about the incident but they knew. ALL/MOST later and older units used a “glow plug controller” which was/is a temperature sensor in the upper water manifold on the right side of the engine. Its’ problem(s) is that it has some electronics encapsulated inside it and because of the extreme temperature changes, would have a premature failure rate. It was a common problem and the most obvious one was when turning the switch to “ON”, the WAIT” light would NOT come on along with the glow plugs as well. You can take a new one and plug the harness into it (without removing the old one just to check) and see if the problem is corrected. Easy fix too. Kascar has a replacement controller (for about $600) with box and a set of very expensive plugs that are not supposed to swell in this application. Bear in mind though that ALL glow plugs will swell if enough voltage is applied to them and left on. Kascar had a re-engineered box and it supplied a different voltage to the plugs or would not stack. This is one way to go but their box is already obsolete! KDS systems (electronic manufacturer that makes pretty much all of these boxes) has a new, improved box part number CR 2699 that eliminates the need for a sensor in the water manifold! The sensor is inside the box itself and it like Kascar’s has a sensing unit inside that prevents the condition known as stacking. If you can find one of these CR2699’s, it will prevent many of the earlier problems and failure rates for a lower price. Also it is a direct retrofit and you just ignore the plug to the old controller and insert a plug into the water manifold 1/2″ pipe thread hole. I hope this answers some questions and helps folks out there. If you have a question and I cannot answer it, I know who to ask! Thanks for reading this, sincerely, Julian Burke----------------------------------------------------------------------------------------- We here at My Hero Customs have found a nice solution to all these smart Box Problems. It is in changing the control of the Glow plug cycling from the Smart Box to the operator of the Humvee. In other words, the guy who is starting the Humvee should decide if or how long to cycle the glow plugs. What we have done is to install a fused momentary button on the dash that has an internal light. Then rewiring the solenoid that is sending the voltage to the glow plugs inside the smart box. Attaching the signal wire from the momentary push button to the small terminal of the solenoid. Don't forget to remove and isolate the original signal wire that the Smart Box was sending to the solenoid. Now when starting the humvee, you don't rely on the wait light. You just push the button for the time you think is required to cycle the glow plugs and then switch on the starter. If the Humvee doesn't start you should be cautious in using the button again. Now your Humvee won't let you down in the middle of nowhere because your Smart Box became a Dumb Box. Your glow plugs will last (as long as you don't fry them) Just limit the cycle to 4 seconds and don't STACK the cycles.-------This article is for information only. If you are not qualified to perform such a task we strongly recommend leaving it to professionals.