ELECTRICAL SYSTEMS TROUBLESHOOTING (CONT)
(Sheet 2 of 2)
PROBLEM NO. 23 (CONT)
This circuit uses a nomally closed pressure switch which opens when accumulator output pressure is about 1,100 psi (7585 kPa). The switch closes
if parking brake release pressure falls below 900-1100 psi (6210-7585 kPa). This causes the PARK BRAKE ON light to come on and provides a path
for the warning horn relay circuit, causing the horn to blow if the transmission is in FORWARD or REVERSE.
The transmission setting is sensed by a microswitch cm the transmission interlock mechanism.
TO TROUBLESHOOT: Disconnect W/R wire from brake pressure switch (do not allow it to touch ground). With engine running; if PARK BRAKE
ON light is now OFF, replace parking brake pressure switch, (see page 2-315). If light remains ON, W/R 16 gage wire between
switch and lamp socket is shorted. See WIRE and HARNESS TESTING, page 2-66.