Volvo Repair: check engine light is on., flash flash flash, black boxes

Question
My "check engine" light has been on for about 2 weeks,but my 1995 850 wagon is running fine.what shall I do about it?

Answer
behind the passengers side head light are 2 small black boxes,1 marked A ,and 1 marked B.on box A there is a small wire insert the wire into the hole marked 2 then turn the ignition key to position 2 but not started.then on the box narked A push the small button for 1 second then release it.the small red light will flash a code back as a 3 digit number.there is a short pause between flashes for a single digit and long pause between the different numbers.example:
a 121 would look like this flash.....flash..flash....flash
write down each code,then after the first code repeats its self then press the button for 5 seconds the light will light when pressing button then go out when released,then the light will light steady again when it does press button fo 5 seconds again,this should have reset the check engine light.let me know the codes. i will tell what they refer to.
         Rege