Can you provide more info, year, mabye some photos of your pack?
it is hard telling with out seeing it, but if your running 240v into it then you should not need another 115v running to it on another set of wires. the box should send the proper voltage to the proper parts/items/motors/lights/controller calling for power.
mabye post some photos?

the other tub sounds like it might have a flow issue in low speed. check to make sure the low speed end of the motor is running at the proper rpm's or check your filter, if you have not changed it in a while take it out and try running the tub with out it on low speed. if it does not shut off then you might need to replace the filter, note: cleaning the filter does not always help a flow issue it is best to replace filters if they are old. If that does not fix the issue check your motors speed. as they get older the motors can slow down some. It might be cheaper before you run out and buy a new one to have it rebuilt. But I would check your filter first. if no dice then move on to the motor and make sure its getting proper voltage to the low speed, if it is check the rpms. When it is shutting off what shuts off? does the GFCI trip? the breaker in the main panel? the Hi-Limit? please give more details cause it could lead me to a whole dif thought.
You can get a Digital RPM Meter Here for cheap and it works well
http://www.amazon.com/Professional-Digi ... 800&sr=8-4I feel like every tech should have one of these for checking motor speeds, it helps disturn questions about the motors speed working properly.