Fuses blow when connected to Truck

[ABChris]

I have a 2005 Jayco 27BH.

Everything works fine when the trailer is plugged into AC and the battery is connected. When I hook up my truck, the inline fuse at the battery blows and the "reverse polarity" fuse at the panel blows.

If I disconnect the battery while the trailer is connected to the truck, it's okay, and if I disconnect the truck and reconnect the battery everything is okay.

The connection to the truck is a factory molded connection (no screw terminals accessible) so I don't imagine that there are any crossed wires there. And, it's a relatively new truck (2011) with factory tow package that worked fine with my last trailer.

I checked the JB behind the battery to see if any of the connections from the truck or battery were loose or damaged, but everything looks okay. I pulled back the wire clamp to look for a pinch, nothing there. the JB is nice and clean, looks like factory, not tampered with.

Any troubleshooting ideas?

[3'senough]

I carry a bully beep tester, makes a beep when you go through the different connections helping eliminate them from the TV back. Sounds like a ground is touching somewhere or the cable is wired incorrectly crossing positive and negative.

[WVDusty]

Sounds to like the battery is hooked up backwards.

[ABChris]

Originally Posted by WVDusty

Sounds to like the battery is hooked up backwards.

The battery is hooked up correctly. The positive is the one with the inline fuse on it, and the terminals are a slightly different size, looks like I couldn't hook up the battery backwards if I tried.

[waynem]

Which terminal of your trailer battery is connected to the chassis? If you check with a voltmeter you should have 12V between the positive terminal and chassis, 0V from negative to chassis.

[ABChris]

Negative ground trailer to negative battery terminal

[waynem]

What happens when your battery is disconnected and you are plugged into the truck? Do your battery powered loads (interior lights, water pump) work? Does your truck have a removable relay for the trailer charging circuit? If you remove that what happens? Sounds like its time to do some measuring with a meter.

[ABChris]

I guess I'll have to pack a meter and try that at the lake next weekend.

Thanks.

[clutch]

Let us know what you find. Something like this could happen to anybody.