I removed the J107 plug and started a game, though only got one ball play as there are 3 other wires (purples) on the J107 that must link to the ball collection tray. If you turn off and start again it says pinball missing so I had to turn off and reconnect the J107 plug.
I checked the fuse at this stage before powering up and all was good.
Then when I turned on the ball collection tray kicked the ball over and the fuse burnt out instantly on this action. I did this twice.

Do you think I have a problem at the BR4 or a short under the playfield? Confusing thing is before I played with the J107 plug and a few hours ago I could start a game and get a few minutes up to 10 minutes of play and the test for flash lamps works fine.

I thought I would retry the last scenario with the balls all in there correct locations, new fuse, with J107 plug in and fired up - now the fuse blows straight away on fire up - does this mean a definite issue with the BR4?

Any clues would be much appreciated.