My experience on the 700 series begins with 90 so I am not sure this applies. Does yours have the small storage compartment above the relay tray? If so remove the surround from the cigarette lighter and remove the exposed screws to remove the compartment.

My 91 745 had a screw in the box that surrounds the radio that allowed the box to be removed once it was unscrewed. The screw was at the top back of space and was accessable once the radio was out of there.

Bulb out relays can be resoldered. Use a strong light and a magnifying glass to look for evidence of hot spots and cracked joints. If I am remembering correctly the one I did had the bad joint on the top- it was easy to access with the iron.

Randy