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Pickups Pickups - Archived Discussions Cabover Campers & Camper Trailers (pickups) 
1377 messages, Last post on Nov 20, 2003 at 1:43 PM
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Have a safe trip--look forward to getting together if it works for you. Ok - The GM Tech. Expert today stated that the Primary bat is connected to camper charging system--(SPECIFICALLY Not Aux.) and the Aux. relay will close when the key is turned ON to bring the Aux bat online to provide the starting/system power if the Primary/Camper batteries are discharged. I'll probably find out some revalation tomorrow and have to EAT these words (which i would be happy to do) BUT the way it looks to me rignt now - I CAN'T BELIEVE GM COULD BE SO INCREDIBLY STUPID. TEST 1- The Aux. bat relay clicks when i turn the key ON and OFF so it is working. Key OFF relay open and Aux. bat is disconnected totaly from everything--i mean EVERYTHING. Key ON and relay closes and Aux. is in the circuit and would be charging if needed. TEST 2- I disconnected the ground to the primary bat simulating a run down Camper & Primary bat. AND WHAT TO MY WONDERING EYES WOULD HAPPEN WHEN I TURN THE IGNITION ON ----- NOTHING - THERE IS NO POWER TO ANY SYSTEM BECAUSE IT IS ALL FEED BY THE PRIMARY BATTERY (Why am i not surprised??). Unless i have to eat these words tomorrow, the Aux. Battery is completly worthless as now provided by GM. 75v |
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A dead main battery would mean you have no power to drive the relay and let the aux battery power the truck. What is connected to the output of the aux battery relay? The input must be the aux battery, but where does it go? I could understand the camper wiring going directly to the main battery. They set it up that way so it would work when no aux battery exists. Can you find the feed wire that goes to the camper wiring, and connect that to the output of the aux battery relay? That would seem to solve GM's little screwup. Mike L |
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The Aux. bat goes to the relay. From the relay it joins the Primary bat at the starter terminal along with the heavy amp wiring. Tomorrow it's going to be GM's turn to figure out how to get the camper power feed from where ever it is now to the Aux. bat. The problem is going to be how to change the wiring harness so that the Aux. feeds to the camper harness and the primary is isolated from the camper harness when the ignition is off. What a bunch of dorks!! Have a safe trip- See ya in IA Loren |
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| n75v111, do you have the camper wiring option or did you connect to stud A? It appears from vinces instructions that the camper option is designed to feed from the main battery through a 40 amp fuse, which he specifically did not do in his installation but used the relay output(at least as I read it). Is this correct vince? | |
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OK, its midnight but curiosity got the best of me. I have the Aux battery but do NOT have the camper/5th wheel wiring option. Did following test: 1. switch off, both batteries connected - measured ~12 volts between stud A and ground. 2. Disconnected ground on Aux battery - measured 0 volts between stud A and ground. This indicates to me that the voltage on stud A (relay output) is coming from Aux battery and is isolated from the starting battery. Thus connecting to stud A will run down the Aux battery but not the starting battery. |
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OK, I think I have it figured out. I took a look at the schematics and I see what they are doing, as strange as it is.
The aux battery relay is only energized when the key is in the RUN position, not the START position. The aux battery is a remote charger of sorts. When you kill the primary battery with your camper, you place the key in the RUN position for a few minutes. The aux battery charges the primary. Then when you turn the key to START, the relay opens to prevent starting current from flowing through it. I can't see any other way to benefit from the aux battery except with a set of jumper cables. That is actually not so crazy because the aux is always kept charged.
This is obviously a stupid system. The only reason I can think why they did it this way is so the camper/trailer positive feed doesn't have to be relocated on trucks with vs. without the aux option.
So Loren, this explains why you couldn't start your truck. You didn't know the turn the key and wait 10 minutes trick. I really wonder if enough charge would transfer to turn over the engine. It all depends on the relative voltage. Anyway the solution is just to move the STUD1 red wire (camper feed) from the Engine Wiring Harness Junction Block to the aux battery positive terminal on the aux relay. No other changes needed. Then you will draw off the aux when stopped and charge it when running.
buzzb, I'm not sure where your stud A is. If it's on the aux relay then you were just measuring the aux battery positive. When the ground was disconnected you no longer were measuring across the battery. Since the relay was open (key off) you weren't connected to the primary battery either. If you meant stud 1 over in the EWHJB fuse box, then somehow your truck got wired intelligently, but I doubt that.
I've updated my web site with the schematics and a brief explanation.
http://members.home.net/vofm/batt/batt.html
Let us know what happens! Vince |
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vince4, the stud A referred to is the output (top) stud on the aux relay. My experiment was to verify that the stud A relay output was connected only to the Aux battery when the switch is off. The owners manual says that stud A is protected by a "mega fuse" (whatever that is) behind the aux battery. Thus factory stud A behaves as it should, like your installation. Relocating the stud 1 red wire camper feed to stud A should work as you describe and be protected by the "mega fuse". It would be interesting to see just what this fuse is but I don't feel like moving the battery. It appears that GMC saved a few dollars by not rerouting the stud 1 (camper/trailer) feed to be from the aux battery when trucks were so equipped. If this is the case as vince4 describes, it is even worse because the main starting battery is not a deep cycle design and its life will be shortened being treated this way. The factory aux battery does not appear to be a deep cycle either, but one could substituted as vince4 did. Please somebody tell me GMC wasn't this stupid/shortsighted. |
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vince - After lying awake till all hours last nite after i posted my #626 message, i came to your conclusion about moving the camper/5th wh feed from the primary bat over to stud A. I'm going to advise my dealer today of the necessary change and request them to "?MAKE?" GM issue a Techincal Service Bulletin advising ALL dealers of this "SCREW UP" and provide PROPER INSTRUCTIONS on ----------- 1) Where to disconnect the POWER FEED in the Z82 Heavy Duty Trailering Equipment & the UY2 Camper/5th Wheel Wiring Provision. 2) Provide proper WIRING HARNESS with SHIELDING and INSTRUCTIONS for SAFELY RE-ROUTING the camper/5th wh feed TO Stud A on the Aux. Battery Relay. Short of getting this out of GM within the next 5 years i will require them to issue a letter for the same so that GM Legal Department can not later claim UNAUTHERIZED wiring changes. Will keep all advise on this move. Loren (75v) |
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The silver salmon are running and the Halibut are biting I hope to be there in a couple of days. This is a picture of Valdez Alaska taken this morning. If you look close you can see some happy campers out there. |
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