Sorry, I have never found a wiring diagram specific to the B230K in its 240 configuration. The best that is available might be this one for the 740, but be aware of differences: http://www.autoelectric.ru/auto/volvo/740/1989/740-89.htm (scroll down)
You may also find something of interest in this discussion:
http://forums.turbobricks.com/showthread.php?t=291753

Is this car new to you? The characteristics of the B230K suits me fine (good pulling power from low revs with its 10,5 compression rate and T cam), but it certainly has some challenges. Beware that this is an interference design, so replace that cam belt in time! The Solex carb has lots and lots of vacuum lines going in and out of it, replacing old and cracked rubber sleeves may be wise. My car had to have a new coil after ten years, the replacement has worked fine for almost twenty years now. The only ignition related problem in later years was that the CPS needed replacing - a common problem, these Hall effect sensors seem to have a certain life expectancy.

Could you describe your running problems?

Erling.
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