Since you have a 94, you can pull codes using the OBD1 port under the hood (see volvotips.com for instructions). Most likely you have a faulty wheel sensor - you can uplug and clean up by the hub, and check to make sure there's no grease on the inside (say from a torn axle boot) side of the hub. Another problem area is the ABS controller which can develop solder cracks. If I recall the controller is attached to the ABS pump where you can try reseating it.

 

Welcome to Volvo Forums Danny

Try this video to help explain the self diagnostics on the earlier models.

 

I have Speedo issues and these lights are on - is there a correlation?

 

yes.

The speed sensor feeds into the ABS controller which in turn feeds the DIMM. You need to check the diagnostics codes to see if its a sensor or the controller. Check out Midwest-abs or Xemodex to see if they have a trouble shooting guide for the 850s. You can also check out volvotips.com if you have a 93-95 850 with the OBD1 diagnostics port for reading ABS codes