On some of the 700/900 series cars, Volvo uses an instrument/accessories lamp in which the lamp is an integral part of the plastic lamp socket. Volvo gets about $8.35 each for these. Our 1988 760T uses several. I had previously replaced the one which illuminates the sunroof and defroster switches with this same method. I just replaced the lamp which illuminates the seat heater switches with this method.

The integral plastic lamp holder and lamp plugs into what is called a diffuser. The diffuser carries the light fiber optic style, to the switches. Volvo also used a plastic lamp holder with a replaceable lamp on the earler 700 series cars. This earlier lamp holder is the same diameter as the later integral lamp/socket assembly, and plugs into the diffuser socket just fine. I cut the wiring for integral lamp/plastic socket ($8.35 combination), and spliced in the earlier socket which uses a replaceable lamp. The replaceable lamps are about $1.99 for two.

The integral lamp/socket is on the bottom of the picture, and the early style socket with the replaceable lamp is on the top.

I think the early lamp holder shown is from the automatic transmission illumination, but they are also used to illuminate the switches on both the right and left sides of the steering column.
--
john