Brake lights are'nt working. on 1993 Volvo 940

Brake lights are'nt working. Checked fuses, stop light switch, wires, etc. all ok. All other lights work as well.

Asked by for the 1993 Volvo 940
There is a bulb check relay in main fuse box, it's round and red. The brake light signal goes into that relay and comes out of it to the brake lights. Check the power in and power out when stepping on the brake pedal. I've seen these fail for just this reason, so that may be the issue.
Good Luck!
Thanks, I beleive thats what the problem is.
We are having the same problem. How do you check the bulb relay to see if it works?