Spa pump problems - cycling off and on

I bought a remanufactured spa pump to replace my leaking one. It's 2hp, 2 speed, 230 Vac. Every thing was working fine before, except for the leak. I installed the replacement pump and it would run for a while, then turn off/on/off etc... After just a few minutes, it would only run for one or two seconds, then turn off for 10 or more seconds. I called the company I ordered from, and they sent another pump (also remanufactured), from the same drop-ship company. It's doing the same thing!

The pump has a ground, a common, and two hots, labeled as low speed and high speed. At the connection to the pump I measure a steady 115 vac across the common and low speed terminals, so I figure the panel is putting out good power. When selected to run on low speed, I don't measure any voltage across the common and high speed terminals. I hooked the pump straight up to my house current 115 vac to the low speed and common terminals. It cycled off and on with this set up as well.

So, did I get two bum pumps? What else can I check to see if nothing is screwed up with my control panel? I really want to get my spa running again, but I don't want to buy another pump if the problem lies elsewhere. It's been too long since I received the second pump (my fault - I let it sit due to frustration) and the company is brushing me off.

Thanks for any help.