MTH Switches have me stymied - throttle overloads after wiring switches for auxiliary power.

You have a short circuit somewhere.

I would disconnect the switches one at a time til the short goes away.

On a larger layout, you would disconnect half the layout.

Then the other half if that did not work to clear the problem.

If that works try half again on the part that still has a short. etc

MTH Switch machines are easy to swap out if that is the problem.

Thanks for the reply - planning to reconstruct layout track section by track section, using a multi-meter on each connection. 
Soldering more drops, and joining sections with wire if needed, it's a small layout so doable. 

Disappointed with RealTrax; I've had connection problems, sections that don't lie flat, misaligned rails between sections, and the new hollow rail sections use a different shade of grey plastic that is shiny, not matte as before.  Used FasTrack in my previous layout, much better except it rusted away in Hawaii climate. 

Alan

Look at your switch wiring, one of them may be swapped. The double switch image won't enlarge enough.

Thanks for all the replies, used multi-meter and fixed a few poor connections. But the problem remained until I switched to using a second transformer to power switches.  I was using Z4000 for track power on one throttle and the 10v aux circuit for the switches.   

I suspect my layout use of three switches joined together and their anti-derailment function is the cause of the problem, but not sure why - yet.  

Alan