If you're still running one of the older engines, you probably have gauge light issues like I did. The little Volvo bulbs(#19923) and sockets(#808175) are getting hard to find at a reasonable price. With a little research I found that the bulbs are a fairly common BA7S type and the sockets were pretty easy to source once I had the bulb type info.
I bought red LED bulbs from
superbrightleds.com/ . They come in red, amber, green and blue, 87 cents a piece.
The sockets came from memotronics.com/ for $3.99 each.
If you go with LED bulbs, you need to get the polarity correct on the socket. Your blue wire is Negative and needs to be on the outside case of the bulb. The white wire is positive and come from the dimmer. It needs to be on the post that connects to the center of the socket.
These LED's are not dimmable. If your dimmer rheostat is jacked up like mine is, move both wires to the double post. Now the light will be on full bright all the time. I went with the red LED's so they are very easy on the eyes at full bright.
The top center gauge has the original white light in it to show the difference between the new red and old white bulbs at full bright.