No-one else has replied so I'll give what little help I can.
The wiring diagram that you were given does not have numbers on it so it's not clear what you mean by the fourth connection or indeed the previous three.
It may seem obvious, but first check that you are not making the fourth connection the wrong way round. This may not be as stupid as it sounds. On an oval layout you must not think of the 'front track' and 'back track' but you must think of the 'inside track' and the 'outside track'. I am sorry if you think that this is insulting but it was a necessary start. (My car handbook says under the "If the car won't start" section - 1. Check that there is fuel in the tank!)
Assuming that this is not the cause then I would suggest that there has to be a short circuit somewhere. Try removing all the connections and making them one at a time in different places. One of your points may be faulty. If the layout is not yet permanently glued down you could disconnect some sections to see whether that isolates the problem.
I hope that will be of some help and that I couldn't be more specific.
The wiring diagram that you were given does not have numbers on it so it's not clear what you mean by the fourth connection or indeed the previous three.
It may seem obvious, but first check that you are not making the fourth connection the wrong way round. This may not be as stupid as it sounds. On an oval layout you must not think of the 'front track' and 'back track' but you must think of the 'inside track' and the 'outside track'. I am sorry if you think that this is insulting but it was a necessary start. (My car handbook says under the "If the car won't start" section - 1. Check that there is fuel in the tank!)
Assuming that this is not the cause then I would suggest that there has to be a short circuit somewhere. Try removing all the connections and making them one at a time in different places. One of your points may be faulty. If the layout is not yet permanently glued down you could disconnect some sections to see whether that isolates the problem.
I hope that will be of some help and that I couldn't be more specific.
