I have a 83 240 D with pencil type glow plugs.I have to turn the ignition switch several times to get the glow plug light to come on, if it comes on at all. I tested the relay with a volt meter get 12.5 on the battery line and across the fuse. I read 11 v on all glow pugs. I hear the audible click of the relay disengaging. Is this a bulb issue? or is it in the ignition sw? How do I determine? Do I need to remove the instrument panel to replace the lamp.