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Problem is the gauge quit working and low fuel light stays on, which means fuel is not transferred from rear tank and you don't have a gauge to tell you when you are out of fuel, even though the back tank is still full. The balance module needs input from both tank gauges to signal fuel transfer relay to turn on transfer pump to move fuel from rear tank to front tank where engine sucks all the fuel from and returns to. This system is obviously only only on trucks with two tanks and maybe only on diesels because gas engines have pressure pumps in the tank(s) to supply fuel injection. There seems to be little understanding of how this works and dozens of variations of tanks, gauges, balance modules etc. There are thousands of pages of problems and discussion of how to trouble shoot and fix this problem on line. Me and a pretty experience HD tech have spent part of 2 weeks researching this problem and are not much smarter than when we started other than thinking we know how it works. We have changed the transfer pump, changed the instrument cluster, checked all the fuses that supply power to the different components (but still don't know where power comes from to supply the gauge), taken both senders out of the tanks to ensure it is not a float hung up(common problem), checked ohms of senders at full and empty(does not seem to be a dead spot anywhere), checked and recorded voltage at all pins in the 20 pin connector at fuel transfer module(don't know what those mean), drove truck to Vancouver and back(2500 km) and had intermittent fuel gauge operation on original cluster(appropriate name for this system!). Does anyone know how to fix this system before I install a Stewart Warner white man fuel gauge and a manual timer for the transfer pump?
 

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How many years later and GM still has some messed up system, didn't think it could get worse than that stupid valve they had in the 80s lol. Finally cut an access hole in the floor of the cab behind the seat of my '85 with the 6.2 diesel so it was easier to change.

I have the four book factory set of manuals for the C/K trucks somewhere around 2K or possibly 2002 models. Would any wiring and such be the same as yours? They might even be newer, I will look when I go out after lunch and let you know later on today.
 

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Thanks AB. Sorry I did not see your post till just now. I/we are still doing some messing around with that fuel system on the Duramax. I have learned a fair amount about the visible and old school electrical part but I tend to just cut it out and bypass the electronics part. This whole balance module thing is way more complicated than it needs to be to have a gauge and a transfer pump from the back tank controlled by a switch or a mechanical timer. In all the work and investigating we have done, have not been able to get it working properly because there are dozens of different versions and models of every component from tanks, sender units that are different ohm ratings (0-90, 90-0, 40-240, 240-40) and different senders that read 0 ohms full and others 0 ohms empty, some have dampening for slosh of fuel, some systems have a transfer pump cutout for when the back tank is empty, some turn on the low fuel light when front tank is low and on and on. By the way all the engine fuel is sucked out of the front tank by the diesel injection system and return is to the front tank. The back tank only transfers fuel to the front tank when the fuel level between tanks is about 2 gallons difference. I have given up on finding the right components to make this work because of all the different components that are not compatible with each other. If you Google this you find endless problems and even more misunderstanding of how it all works and almost zero solutions to it. We found a Stewart Warner gauge that is 40-240 ohm and works with the original GM sender, except it reads backward. You can't switch around wiring because the problem is in the variable resistor that is reading 40 ohms empty and the gauge is made for 40 ohms full. You could get a gauge made for 40 ohms empty but we wanted to get it put back together, so we made a new float rod that extends off the other side of the sender rheostat which now gives us the full tank reading of 240 ohms at full tank. If that makes any sense!! So now we just have to wire a power wire to the transfer pump with a switch in the cab. And remember to turn it off!! That's where a mechanical timer might be worth adding in to the transfer power supply. Also I think we are going to try to hook the back tank sending unit direct to the oem dash gauge, bypassing the module with all the balancing and switching relay crap. It will be nice to be able to monitor fuel level in both tanks.

Thanks for your offer to look up this system in some manuals. It might be interesting to see what the manuals say but on the other hand I am about fed up with experimenting with this whole system and think we will be able to make it work with standard Stewart Warner components which get the job done and make a lot more sense to me. There is a strong similarity in this balancing module system since back in the early 90s GM pickups, ever since they had the front/rear tank selector switch. That probably would not work that well with a diesel! I have found that the wiring and plugs are different between 90s series and newer style into the early 2000s but there are a lot common things through the 2000s. Except the hundreds of differences I mention earlier. Trust an office building full of engineers to make something more complicated than it needed to be. LOL!
 

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One of the simplest fuel transfer systems I’ve ever seen was on the first new snowmobile with two tanks. Simply, no atmospheric vent and a sealed cap on the front tank, that main tank vent was instead attached to the outlet on the second tank and that second tank had an atmospheric vent. The fuel gauge was in the front tank only and registered 100% full until the rear tank was empty. It worked like a charm unless you added fuel to the rear tank only on a 1976 Pantera.
 

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Drill and tap holes in the bottom of the tanks and run a transfer hose? It would only take a 3/8" hose.

Just an idea...
 
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