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1377 messages, Last post on Nov 20, 2003 at 1:43 PM
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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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Gm Tech. saying that Aux. bat not really intended to function with camper -- Dah!!! Stupidity at it best. I sent a letter in part repeated below to a Gm Corp. Sales Planner contact that provide lot of answers during my six month delivey wait. --After considerable discussion over the Internet last night it is clear that GM should have ran the Power Feed for the Z82 Heavy Duty Trailering Equipment & the UY2 Camper/5th Wheel Options to the auxiliary battery relay Stud A referred to in the Owners Manual on page 4-81 (terminal 'L' in the schematic you provided). I would request that GM be asked to ISSUE a TECHNICAL SERVICE BULLETIN when customers order the Auxiliary Battery TP2 Option in conjunction with Z82 Heavy Duty Trailering Equipment and/or the UY2 Camper/5th Wheel Wiring Options ADVISING all DEALERS & CUSTOMERS how to properly and SAFELY reconfigure the power feed wiring from it's current location in the Primary Battery Circuit to the auxiliary battery relay stud A.-- His Response -- "Thanks for your letter explaining wiring problems with the TP2 Aux. Battery option. I can tell you that the factory option is on stop right now for revisions. The revisions will most likly result in a service bulletin to modify those already out. I'll send you another reply if I have any updates. In the mean time I will forward your comments to the brand Quality Team." 75v |
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| Be SURE when the red camper lead is connected to stud A to put an inline fuse of the proper size in. Otherwise your camper/camper wiring harness is only protected by the "mega fuse" (whatever that is) between the aux battery and stud A. I would hate to find out the hard way that it is way over amperage for the red camper lead. | |
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Oh the saga of the auxiliary battery is winding down. Hmm, we've about covered Maid-Rites too, what's left? When Mike gets back he can tell us all about year 2001 Maid-Rites, I hope he wasn't let down. 75v, I don't know how important it is to you to have the factory do the fix vs. living with it the way it is. Since it's not likely anything will happen soon, I would just go ahead and make the change myself. If you do a good job they aren't going to make a fuss unless something in that system goes bad, and maybe even not then. One out you have is to do the work such that it can be restored to factory. Don't cut off the ring lug on the red wire, just use a bolt to connect it to a second ring lug (or use a breaker like I did). Other than that it's one wire going across the engine bay. I agree with buzzb that the non-deep-cycle battery won't hold up to RV use for too long. Maybe when GM moves the wire they will start putting DC batteries in the aux position. I guess GM's thinking is that the extra battery really is just an auxiliary for self-jumpering or heavy loads and doesn't have anything to do with RVs. |
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| Another way to wire the batteries is to install a switch for the batteries. They are readily available at RV shops and battery shops everywhere. I put a dual battery setup in my boat and the way I tied them together was with a switch. They are a make before break switch and it allows you to run on one battery or the other and it allows both to be tied together. Took about 1/2 an hour to install. | |
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