Your proper switches, assuming they work correctly, are the two paddle-like switches that say "heat" and "def". Because they have the resistor on the back they should have either 2 or 3 speeds. Your hot wire in 12V should go to the reducer-resistor first and then to these switches. Your switches with round knobs are not correct but may work well.
The correct switch to the Trico Electro-Vac is a round red knob that says "VAC" and the knob lights up when turned on. The knobs are kind of rare to find. My 50 COE came with an Electro-Vac and I found the correct switch years ago. The unit is installed in line with the vacuum line going from the intake manifold to the wiper motor. When energized (turned on),if the unit detects loss of vacuum, the electric motor is turned on driving a vaccum pump. If the switch is on but no vacuum loss is present nothing happens. My truck lives at over 6000 ft elevation and I get 11 inches of Hg vacuum with just the Electro-Vac. That is enough to run the wipers without the engine running and is equivalent to about 13 inches at sea level.
To me it is amusing that Trico produced these units. Trico made millions of wiper motors for many many manufacturers and was certainly aware of complaints about loss of wiper function at wide open throttle or driving up hill. Instead of an electric wiper motor, they designed this curious little device that used an electric motor to drive a vacuum motor so they could continue selling vacuum wiper motors. Mine functions quite well, although in Arizona I confess I have only used it sparingly. As I like to say, all part of the charm of driving an old truck.
Kent
PS: To clarify my comment in the 3rd sentence. I doesn't matter what order the resistor is in wiring your heater/defroster. What matters is the total resistence of the circuit, in terms of protecting your 6 volt motors. It would be simplest to have the hot wire go first to the resistor so you don't have to have multiple resistors.
Last edited by Lightholder's Dad; 10/26/2026 9:37 PM. Reason: clarification
