Jim,
Wasn't aware of the dual motor setup. Assuming that each motor has an independent switch, then problem likely to be in common area. If single switch controls both motors, it would be my primary suspect. Wiper motor speed is normally controlled by applying either voltage or ground to the appropriate motor inputs. From what you state, it sounds like you are losing the low speed signal from a common source, apparently the PC board you referred to. Any PC board/circuit in the motor would be the same for both so I don't see how that could be cause.
You may want to access the connector at the wiper motor and, using a volt meter or light, see what you are getting for voltage or grounds when on high and low speed. If you hook voltmeter/light up to ground as common and don't see any signals when selecting speeds, ground is probably being switched, rather than voltage. Then hook up your mete/light common to 12V.
Not sure how your washer motor circuit is wired. On mine, pressing the washer switch turns the wipers on low and activates the pump. However, i can also activate the pump when the wipers are on high. You may want to try that if you haven't already. That would tell you that pump power is dependent on the wipers being activated. If the pump doesn't run on either setting, I'd focus on the pump. You can use a voltmeter/light to see if you are getting power to it, before replacing it.
Hope this helps some,
Steve
