Maintenence Electrical Troubleshooting Mercury Arc Lamps "J&L Projection": We have had much discussion as of late regarding the testing and verifying of mercury arc bulbs. We have... house and Mercury arc bulb. Put the red lead on the center post and ground on the outer rim of the lamp socket. Activate the lamp house safety switch "depress the micro switch... voltages and your mercury arc bulb does not start or stay lit is safe to say that your bulb is bad. If either of the voltages is out of spec you have a run circuit electrical problem...