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Monday, July 19, 2010

Dead Battery on Towed Vehicle

Hey Doc! Every time I tow my GMC Sonoma 4x4 pickup more than four hours without stopping to start the truck for a while, my battery is either completely dead or just barely turns over the engine. Is there a fuse I can pull during towing to reduce battery usage?
Tim, (Reno, NV)
Tim, a lot depends on how your GMC was wired for towing and of course, what type of on-board equipment you are using, I. E., auxiliary braking device, lube pump, etc. If all the power for turn signals, stop lamps and running lights originate with the motorhome, as they should, and no on-board power is required by the pickup, then the simplest method would be to install a battery disconnect switch for all circuits contained in the truck. This can be accomplished with a simple knife-blade manual switch or a simple electric solenoid mounted near and connected to the battery on the truck. Both are available at any well-stocked RV accessory store. 

Either device will enable you to fully disconnect the truck battery while towing. I do recommend breaking the circuit on the ground side. However, it’s possible there is a drain on that battery caused by the tow wiring. Some circuits may require diodes to prohibit current draining or bleeding while towing. Without seeing the wiring or the methods employed as it stands right now, I’d only be guessing. I’d recommend a trip to your local RV service center to check out the existing wiring configuration and possibly have that bothersome drain eliminated. I’d hesitate removing any fuse until it can be ascertained that that circuit (protected by that fuse) is not required by the truck while towing.


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