when looking at my diagrams, i see a white/red wire which leads to the ignition coil... that would probably be the one you would want.... And I've always thought that you would test for a negative pulse here when cranking/engine running... (it may be too fast for a multimeter to pick up when the engine is running...) so you would connect the red lead of your multimeter to a known + and connect the - to the white/red wire, crank the engine, and while cranking, the voltage should fluctuate from 0 to 12v... It looks like this White/Red wire is located right next to a Red/White wire...

if you'd like, i could upload the instrument cluster diagram...

Cliff Scott
89 740 16v