the problem is not electrical. It is mechanical. the lines are leaking in the caster assembly. this is complex and requires a great deal of work. it is also quite expensive. you will need two new master cylinders a slave cylinder new brake compression fittings, a caster swivel assembly, and caster brake manifold. If you do not repair all of the items the system will not work. Parts will be around 800.00 and if I did the work it would take me 6-8 hrs. (I have been a Tech for 30 years) it is a serious problem. But if you fix it correctly it will not bother you any more.call if you need me further.

Do you get a fault code when this happens? If not I would start by checking the brake switches and move on through associated wiring.