I'll hear it (barely) firing up while the car is running but only occasionally. The car often sits for 1-2 weeks or more between starts and the pump probably activates less than half of the time when I start up. My pump comes on as needed, which is not often. Unfortunately my pump is mounted in a location that makes it a huge hassle to access, so I can't inspect it to see where it could be adjusted- I don't recall seeing anything like that before I installed it. Also any ideas why the lights dim for a second? I cleaned the contacts and used 10 gauge wire to run the pump. Is this something with the regulator that can be adjusted or is this just how it normally operates? Seems odd it just keeps switching on and off even though it has plenty of vacuum. It also has been causing my interior lights to dim for a second every time the pump cuts on. I actually pulled more vacuum in the system via a hand pump up to about 24" and it still cycles on and off. So the vacuum gets up to about 20" and then shuts off and turns on about every 5 seconds. I wired it using a relay directly to the battery via the splice bus behind the battery. Q: Is the pump supposed to constantly cycle on and off? I installed this on a '67 Pontiac 400 with a big cam to run my newly installed power brakes (really should have left them manual, but here we are).