Help guys!

I just did a front brake pad replacement on my 740 GLE Wagon about 6 weeks ago and the goofy brake light lit up about 200 miles later! I never diconnected any lines, i just use a c-clamp to compress the piston back into its housing. I have Girling front brake calipers. I looked at the wiring connection to the master cylinder, and upon messing with it the light went out. No sooner than doing so the light illuminated again! What might this part be, and can it be removed with out allowing air into the system? It is a small plunger like device that plugs into the master cylinder line connection, in addition it has one wire that gives it electrical current(costs/name of part). Would bleeding the air out of the system help? The pressure feels ok, and i have not lost any fluid. I may need ani-rattle clips? Would these clips cause this light to come on? All of your responses would be appreciated.


Thanks in Advance

89 740GLE wagon 375,000 miles