F250 Requires Trailer Battery

[Penner]

I've run into something I have never seen before. I have a 2005 F250 V10 with IBS to tow a 2015 Eagle HT 28.5 RLS. After replacing the battery in the Eagle I discovered that the clearance, turn signals and brake lights on fiver won't work without a battery installed towing with my F250. Thinking something was wrong I then connected my Eagle to my brothers older Dodge that doesn't have IBS and all lights worked as expected. Everything is connected via 7 way plug. Is this normal? I never heard of this before.

[dennis b]

Longshot here. If never towed before there is a relay that must be installed on truck.

[Penner]

Thanks. Truck is already set up for fifth wheel towing from previous owner and factory tow package. I never noticed this since I always towed with a battery installed in fiver and lights all work correctly. I accidently discovered that the exterior lights won't work until I was changing out battery. Is it possible that the factory IBS and trailer fault system on TV requires a battery installed in fiver to properly function?

[Flyrotor]

Most likely it is a grounding issue, for some reason is solved with a complete circuit that is provided with a battery installed... a long shot, but maybe....

[Jagiven]

X2 on the ground. Also double check that you did not reverse the polarity. Check both the wires, and the reverse polarity fuse in the 5ver's fuse box.

If you do not have a multimeter, and if the 5ver is not connected to shore power, you can take a spare 15 amp fuse and plug it into the 7 pin wire harness across the keyway. One pin is the AUX power and the other is the marker lights, just need to complete the circuit with a fuse, and this will turn on the marker lights. No lights now power.

[brwarrior]

Does the IBS say everything is ok? Former employer had a F550 and we started having disconnect issues. Dealer was at a loss. We found the aux trailer fuse was blown.