HCU Push/Pull Diagnostic Information

Workhorse Original Push/Pull Switch - Part# S446 280 001 0

Out 4560 ohms - Neutral 1560 ohms - In 560 ohms

Third Generation is opposite - WABCO Part# S446 280 002 0
If your switch works like this one you have the wrong switch installed.
Second Generation Push/Pull -  In 1556 - Neutral 4530 - Out 580

Unplug the dash switch and check for resistance across the 2 pins:
1) resistance with valve in the IN position=
2) resistance with valve in the NEUTRAL position=
3) resistance with valve in the OUT position=
Plug the switch back in and check resistance from pin 11 on the ECU 31 pin connector to chassis ground:
4) resistance with valve in the IN position=
5) resistance with valve in the NEUTRAL position=
6) resistance with valve in the OUT position=

Wabco-NA.com
HCU Manual - MM01401

All push/pull button part#'s at the time this article was published:

Parking Brake Switch
Kit Part Number	Application Information
S446 280 001 0	Kit contains second generation switch (with new Deutsch connector). S446 280 790 4 (Dash Knob) not included. For 8 coil and 10 coil application.
S446 280 002 0	Kit contains third generation switch (with Deutsch connector and redundancy circuit). S446 280 790 4 (Dash Knob) not included. For 8 coil and 10 coil application.
S446 280 012 0	Kit contains second generation switch and short bracket. S446 280 790 4 (Dash Knob) not included. For 8 coil and 10 coil application.
S446 280 013 0	Kit contains third generation switch and short bracket. S446 280 790 4 (Dash Knob) not included. For 8 coil and 10 coil application.
S446 280 022 0	Kit contains second generation switch and long bracket. S446 280 790 4 (Dash Knob) not included. For 8 coil and 10 coil application.
S446 280 023 0	Kit contains third generation switch and long bracket. S446 280 790 4 (Dash Knob) not included. For 8 coil and 10 coil application
S446 280 790 4	Not included in the parking brake switch replacement kit. For 8 coil and 10 coil application.