I recently went through the same ordeal - Lots of good help here. Do search and go back for " eons ". Also do an extendted search at www.deja.com for volvo Hall sensor. Since my car was disabled I took a digital VOM with a diode test function and momentarily check for continuity using various terminal combinations (my dead one showed none) and the one that did I bought. Before installing the used distributor in, I pulled the hogh voltate coil wire from the distributor and put near metal so it would spark. I then temporarily hooked up the plug to the distrubutor (not installed in engine yet , and turn on the ignition (not start position) and rotated the distributor by hand. I got spark and heard the fuel pump turn on. OK then turn off ignition the installed the distributor and set the timing.

Good luck