Pre-glow issue revisited

After "fixing" my no pre-glow light issue, I drove the car a couple of times. I drove to work yesterday (4 miles) and parked the car in the garage. When I left work at 5:30pm, the pre-glow light remained dark. BUMMER!

I opened the hood and the glow-plug relay box and looked for any obvious problem. Seeing none, I disconnected and reconnected the two plugs. Still no pre-glow light. I loosened and tightened the screws holding the strip fuse in place. As I tightened one of the screws, the screw driver toughed the body of the car and there were a few sparks. I thought, oh, let me try starting the car now. Voila. We have pre-glow, we have ignition.

Not being very skilled at automotive electronics, I assume that there is a ground wire that is loose. I'll check the maintenance manual... scratch that... I'll do a web search to see if anyone else has documented the solution to this problem. If you have any suggestions please let me know.