I pulled my TT from storage the other day and hooked up a freshly charged battery. First the positive terminal then negative. I noticed quite a spark when I connected the negative terminal, but thought that should not be a that unusual. But I double checked the polarity as OK just to be sure.I entered the TT and found that all my 12V endpoints do not work. Went to the fuse panel and found both main 40 amp fuses blown. Anyone have any ideas what would cause both main fuses to blow. I will go ahead and replace them today, but am concerned I might have an underlying problem. Though I am not sure what that would be.

If both polarity fuses blew you need to recheck the polarity. Don't go. Y the color of the wire, find the one that goes to ground and hook that one to the "-" post.

Sounds like a short circuit that was open until you made the second connection. If the rig was grounded connecting the positive side of the battery would have blown the C/B also.Of course, where the short is...? Anything different from when you put the rig away? Any new work? If it was me I'd hustle the RV to my dealer who has smarter people working there than I.

Those are not polarity fuses, but they mite have blown if polarity was backards.Otherwise look for a dead short circuit. Remove all other DC fuses, then check again. Use process of eliminization ! :)

Do you have a wire that was on the battery that is now disconnected and laying on the frame? If that circuit was powered that may have caused a short circuit. To blow the 40 amp main fuses, you would need to have a dead short or reversed the polarity.

A piece to the puzzle. I put a meter on the battery. This polarity is reversed.This can happen????? I did not think a battery could reverse polarity. How does that occur?Maybe a short in the battery. Is it possible that I charged the battery with reverse polarity? How would I fix that?

Blown fuse help | Good Sam Community

MrWizard
Moderator
May 15, 2015
Take another look at the battery and the wiring
When you connect the trailer if there is a white wire and a black wire
The WHITE is the negative ground, and black and all other colored wires are the hot wires
time2roll
Nomad
May 15, 2015
js6343js6343 wrote:
Its the battery. I pulled it from the TT. Walked the battery into the garage. Put a meter on it. The posts are reversed in polarity.
Fully discharge the battery and charge with correct polarity. Once discharged you may need to jump start the battery depending on the charger to get it going. Depending on your needs the battery may still function. No harm to try.
RJsfishin
Explorer
May 15, 2015
To reverse the polarity, the battery must have been near stone dead, and it must have been a manual charger. The battery being stone dead,....for how long ??? would do the damage, not reversing the polarity. Like said, turn it back around the right way, it will be ok,.....or as ok as a dead battery will ever be.
js6343js6343
Explorer
May 16, 2015
Well here is the follow up. I have a small 1 amp motorcycle battery charger I use to trickle charge the TT battery. I must have reversed the polarity and left it to charge at 1 amp for several weeks. This reversed the polarity of the battery to -2 volts. Enough to blow both 40 amp 12 volt polarity fuses. I also noticed that my electric tongue jack was working in reverse (up went down and down wet up) but did not really thing to hard about it at the time.

Well after seeing -2 volts on my meter after I pulled the battery from the TT it all made sense. Charged it with the proper polarity today and we are back in business. Now we will just have to see if it will hold the charge this weekend or whether I really did toast it.

Weird. Never heard of such a thing.

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