If you want to use the #3 pin you will have to view it with a DVOM that has duty-cycle readings or possibly with a tachometer.
The signal is a 12v square wave with constant frequency and a varying duty cycle. A voltmeter will read this as either 12v or the average depending on the meters method. If you have voltage you probably don't have an OVP problem though.
What you really need to be looking at is the current being fed the idle controller. It should be around 6-700ma at idle. It should raise 50ma with the A/C and should go to 8-900ma when the throttle is openned. A bad OVP can cause the current to drop to as low as 3-400ma before the engine dies. This kind of OVP failure is the exception to what I stated about OVP as a result of voltage at the pin #3. In this kind of failure the OVP isn't dead it is just a poor circuit.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician