The brown wire IS ground, you should NEVER see any voltage on either one.
Originally Posted by
onehundred80
When the light is lit up there is power in the ground otherwise it will not work.
You do not want to see power in the ground wire in your home wiring, common yes, ground nein.
The two bulbs share a common ground so my guess is the ground wire between the two housings is broken, add one at your leisure.
I stand by my original statement. If you place a voltmeter red wire on ANY ground wire in the car at ANY point ( with the voltmeter black wire connect to a known GOOD ground ), you should NEVER see any positive voltage !
ground = earth = 0 voltage