I had to take my 12 pin off the caravan and fit a 7 pin to mount a new plug and play brake system. When I put the car in reverse with the caravan attached, the fuse blows and I have no reverse lights on the car, no reverse camera screen in the car and the car is stuck in park, have to manually release the shift. Any ideas please what to check?

Roscoe, make of car, make of caravan and any other pertinent information will be helpful.

G'day Roscoe,
Welcome to this forum where some of us have experience, some are still learning in the problems that "houses on wheels" can throw at us occasionally + those of the car! I hope you will enjoy your time here, perhaps share something of your experiences too.
The forum has many pages, segments - have a good look around them. You might even get a good laugh too. Also there is a Search, Advance Search that may be of assistance too.

I assume you did the wiring rearrangements. The 7 pin common connections are the same for both the 7 & the 12 pin plugs. Some questions -
1. It worked ok before the brake rearrangement?
2. You copied the wiring correctly?
3. You didn't get a strand of a wire that didn't go into the correct connector & may be touching its neighbour - I suspect something askew with pins 2 & 3 (2 is reverse, 3 is earth)?
4. Do you have a multimeter? If not they can be quite cheap from various companies including Jaycar. You may need the assistance of another person.

I'm curious about the brake system you've installed. Is it the safety Brake-away system?

Let's know the answers & we'll try to get you out of trouble. The worst case senario will be that you'll have to see an auto electrician.