The pump status input to me is soldered to a PIC pin which switches a relay
on / off.
Since this is an Arduino forum, we should also recommend that you can the PIC, and
switch to Arduino.
Besides what everyone else mentioned, you also need a reverse diode across the relay
coil, to prevent inductive spikes on switch-off.
Also, for situations like this, you need to implement several of the common fixes to get
the best results = diode across relay coil, snubbers on motors, star-grounding, low-pass
filters on ADC channels, extra decoupling [bypass] caps on the microcontroller. Each of
these solutions helps in its own way, and there is no magical one-thing-fixes-all.