Originally Posted by boondocking
The solar output will not hurt your tow vehicle. A typical alternator can put out as high as 15.5 volts.
I agree with what boondocking has said. I have never checked on my current truck but on my previous truck when I click the tow/haul button it put the alternator at a higher output in the 15-15.5 range. I towed 7-8 hours at a time with that truck in tow/haul. Also items like high beams will easily force the alternator to put out over 14 volts.
The power line going back to your tow vehicles charging system is also quite small and the amount of power going back to the vehicle is not going to be much. If it was an issue I would believe the fuse for that supply would fail in an overcharging situation.
If you are still concerned, put a shut off on the vehicle charge line.