My 2005 tc horn stopped working completely. Not at the wheel pad or panic button. Took the horn off and tested it via the factory connector and the horn works. Took voltage reading on the car side with the horn getting approximately 11.5 volts. Now I'm scratching my head

 

The horn system is operated via grounding circuit to make the horn work from the steering wheel. I had a thread about this same situation on my 04 T&C there is a ground circuit in the fuse panel/TIPM that goes bad, and proper fix is the replace the under hood fuse panel. I was able with the help of a member here to track the proper color code wiring for my year and make a jumper wire to bypass that printed circuit in the fuse panel/TIPM to get my horn working again...been at least 6 months now and all is well.
Look up my member profile and search my posted threads, when you find that thread READ IT...it will help you out. I just can't say for sure that your year color code and wire pin location are the same as mine.
Good Luck!

 

Here's the weird thing. When I run a voltmeter between the two wires of the horn plug, I get 12 volts with the horn button pressed. I hooked the horn straight to the battery and it toots. I then took the voltmeter probes where I get power in the plug and hooked them to the horn. Nothing. How can this be. Power to the connector but horn dosent sound. I'm scratching my head.

 

YUIP! I'm not going to detail it all again as it's been some time now to remember each step. There are you tube videos on this same problem also. I was getting quite aggravated myself with the problem and especially when I tried another fuse panel from my parts van and got my horn back but lost my high end radios sound in the swap. And this type problem affects more Chrysler/Dodge products than just the vans, it is a poorly sealed printed circuit board in the fuse panel out under the hood!

 

I do recall that one end of the jumper wire I made up went into a spot of the horn relay on the fuse panel, in between the plug in relay and the "board" and then the other end was spliced into the proper color coded wire for horn circuit (a ground wire) that comes out of the bottom of the fuse panel thus bypassing the printed circuit of the fuse panel for the horn.
BEFORE I had gone so "in depth" on fixing the problem, yes I tried replacing the horn relay with a known good relay, and that didn't help any either. You'll find it is what I posted of.