I'm looking for the metal piece that fits under the dash and has the knob attached to turn on the wipers. I'm returning my '48 sedan to vacuum wipers and have a motor but not this part. Please let me know if you have one you are willing to part with. Thanks

I might. Still need it?

I was just going to start a new thread about this very same subject, so I'll just tag my issue onto this one. Now that my gauges are out and off for repairs, I can easily get to my vacuum wiper control, which is leaking. The wipers still work, but when I turn the control to "off", the wipers quit and the leak starts. I know it's the control leaking, as I can put my fingers on it and almost make it quit. I had it out and apart, and it seems to me that there should be a gasket between the two "halves" of the control. I see no information in my '48 service manual covering this. Does anybody know what the inside of this switch should look like, and does it have a thin gasket?

No gasket. Just clean and make sure their is no trash between the two pieces. Might stretch the spring a little to put more pressure on the fit.

As to the leaking. When the wiper is off, their is a constant vacuum through the wiper motor (small hose) to hold the wipers in the "park" position.

Might read this old thread.
https://vccachat.org/ubbthreads.php/topics/255408/re-wiper-motor-vacuum-1948-hoses.html#Post255408

I'll try your suggestion, then I'll probably end up blocking off the park feature like the above thread indicates! Thanks for the great info!

OK, I tried plugging the small line that provides the vacuum for the park feature. I plugged at both the motor and control ports. Still hissed when off. I reached out to the Wiperman and he recommends ditching both the motor and control and replacing them with a new motor with a cable operated switch. The switch will have to be mounted in a non stock location, keeping the stock switch as a dummy. Has anyone done this and what did you think of it? Wiperman no longer provides a block off plate conversion for these motors. Is there any better solution to this problem? Wiperman says this particular Trico design for 46-47-48 Chevy's is no good...This is most frustrating, as I'm trying to keep this car as original as possible.

My two cents. Since your motor works, keep it. You blocked off the small port and still hear the hiss through the switch. That tells me air is probably entering by a gap in the two halves because of slight wear, warp or crack. Take the piece with the 3 ports and drag it across a fine file or fine sandpaper on a flat surface just to clean it. Go easy! Get the two pieces to fit and apply a light coat of grease between and put it back together. Install and enjoy.

Best of luck!

Oh, make sure the hoses are good and tight.