[Richard_G]

Pump running on and off without the brakes being touched is a symptom of an internal leak in the brake modulator. Often caused by rust where old brake fluid that has absorbed water has been left in there. A full flush with new DOT 4 fluid might cure it, otherwise you'll need to strip and rebuild the modulator.

 

[Richard_G]

You can easily check for an internal leak. Disconnect and plug the hose from the reservoir to the pump. Rig up a temporary reservoir to feed the pump and switch on the ignition. If the pump running fills the original reservoir, then you have an internal leak.