I agree with both of you. It is more likely an electrical issue, ie: low voltage. I would clean all the harness plugs, and connectors, including the main plug in the rectifier, and the chassis / engine / battery grounds.
Also do a static voltage test on the battery (12v), and a running charge test (14V), then a load test (switch on the lights / 13v-14v)
If it is still an issue then perhaps (not very likely) the pressure sender is faulty.