Alright then: disconnected all TB (1, 2 , 4, 5, 6 - pump 1 & 2, circ pump, heater & ozonator).
Still trips the breaker.
I had replaced the gfci breaker with a newer one (spa is 14 years old and the local electrical wholesaler luckily had 1 that fit the box).
For kicks and grins I disconnected...