I purchased a used American Spa with EM 103 controls. Unfortunately it sat for almost 2 years before I got around to hooking it up. The previous owner had just installed a new motor and assured me it was working when I bought it. (I actually saw it working weeks before I bought it) Anyway, I disconected every device there is and it still trips instantly. Is there anything obvious I should check? It has a timer for the filter, controls for the heater, and a switch for system power.

The Brett 103 is pretty simple, but I would consider double/triple checking your electrical hookup before looking at component problems.

Most likely cause for this is miswiring either in the controller, at the remote disconnect (if you installed one), or in the breaker box where the 50 amp thingy resides.