In my case, the vacuum was fine but the switch needed adjustment. My "lazy" way: get a pair of pliers and gently bend the bracket holding the brake switch (the switch with vacuum hose) downward a tiny bit . This fixed my problems. where is the break position switch, out in the engine comp...

how does one test the components once you find them.
found and looked at the one under the battery, and then ?
found and looked at the solenoid coming off the throttle, and then?
found and looked at vacuum servo, and then?

does anyone have an Volvo service manual on dvd for sale? 1998 v70xc