power to heater hotwater vacum control valve

[Novasmithjohn]

where does the power to the vacum control to shut off the hot water when the A/C is on max? im getting only 5 volts at the plug 1999 tahoe LS

 

[east302]

Here’s the diagram. It should be battery voltage to the solenoid. Is that 5V measured using the connector’s ground or the chassis? Ground G105 is at the harmonic balancer.