a/c and brake questions

[ozbowhunter]

I am just about finished the truck and have a couple of small problems
and want to get your ideas before I go and do more then I need to
regarding the AC the system seems to be holding pressure but the compressor keeps clicking on and off fast im thinking this might be a bad low pressure switch what do you guys think
as for the brakes when I start the truck the brake light comes on and stays on I have replaced the rear slave cylinders and rebuilt the front brakes I then bleed them and still the same problem I know its not the parking brake switch as it isn't on but when I disconnect the front switch it goes off could it be something to do with the vacuum assist ? if so where do I start any help will be great