You'll never will be able to sense 5 volts, not even pulse, because the pulses are really 12 volts. But the averaging of the pulse going in and out will make 5 volts.

Each VL got its own pulse rate.Is hard to find one equal to the other. You can just test it with a test light or analog multimeter. A digital multimeter will get an erradict reading due the sampling rate for the reading non matching the VL pulses. Althought if you get 0 or fixed 12 VOLTS still on a digital multimeter its damaged on either of those stages. A test light or analog multimeter is more trustable thought. That will tell you is good or bad, but no if the voltage is correct. You will need special testing tools for that, like an osciloscopy

and absence of ground on VL will feed full 12 volts and burn the gauges, so is MANDATORY get the VL correctly grounded

The condenser, PER PN DESCRIPTION its a noise suppressor, but it could work as a buffer power? Actually the VL can work without the condenser and I have seen several cluster without it