20 .
TROUBLESHOOTING GUIDE
LRST40EST
Test Equipment:
1 . 0-5000 psi pressure gauge
2 . DC voltmeter/ohm meter
3 . DC amp meter
4 . standard mechanics tools
Note: Please refer to the electrical diagrams and hose connection drawings in the liftgate’s owners manual when
troubleshooting . This guide is only for standard Thieman liftgates . Special liftgates with options other than those
in the owner’s manual will require special diagrams for troubleshooting . Read and understand this entire guide
completely before doing any troubleshooting . Certain listed problems may be related to other problems listed so
a comprehensive knowledge is required before proceeding .
1. Problem - Pump motor will not run in the raise or lower mode
Causes
a . Tripped circuit breaker
b . Blown 20A fuse
c . Improper battery cable
connection or improper
ground connection
d . Defective or
undercharged
battery(ies)
e . Defective or improperly
wired raise switch
f . Defective or improperly
wired lower switch
g . Defective or improperly
wired solenoid start
switch
h . Defective pump motor
Correction
Reset the circuit breaker located within 2ft of the liftgate supply battery(ies) .
Replace 20A fuse(s) . Each control cord should have a 20A in-line fuse on the
black wire, where it connects to the 2ga battery cable at the motor start solenoid .
The “at rest” voltage for the batteries without the engine running and under no
load should be at least 12 .5V, and this voltage should be seen on the heavy 2ga .
battery cable, where it connects to the large terminal of the motor start solenoid .
The minimum voltage between the motor stud and ground is 10V at maximum
conditions, with pump motor, batteries, and cables under max . load . If the
voltage is dropping below 10V under max . load, bad connections may be acting
like resistors and causing larger voltage drops than expected . Check voltage
drops with system under load at different locations between the liftgate and
battery source, to locate bad connections along the battery cable . Trace ground
cable connections also to locate improper connection(s) along the ground path .
Make sure the ground cable is installed going from the 5/16 tapped hole in the
aluminum pump base marked GND to the liftgate mounting plate (scrape paint
to bare metal for good ground) . The ground cable from the batteries to the
frame must be a heavy 2ga cable that is connected to bare metal on the frame .
Replace any damaged cables and repair any bad connections .
If proper voltage is not present, load test batteries and replace any defective
batteries . The battery(ies) on the vehicle should be that which has a minimum
180 amp reserve capacity .
Check for voltage on the black wire at the control switch . If no voltage is
present the black wire from the motor start solenoid is loose or broken and
needs repaired . If voltage is present then check for voltage at the white wire on
the switch with the switch in the "UP" position . If no voltage is present, replace
the switch .
If the pump motor runs in the "UP" position but will not run in the "DOWN"
position, then check for voltage on the white wire at the switch with the switch
in the "DOWN" position . If no voltage is present replace the switch .
Check for voltage on the white wire at the motor start switch when the switch is
activated either "UP" or "DOWN" . If no voltage exists the white wire is loose or
broken between the switch and the motor start solenoid . Check that the purple
ground wire on the start solenoid is connected properly and there are no bad
connections . If there is voltage on the white wire and the coil does not energize
or if there is no voltage on the motor side of the solenoid or a large voltage drop
present across the large terminals of the motor start solenoid then replace the
motor start solenoid .
With the switch activated in the "UP" or "DOWN" position and the motor start
solenoid is activated, check for voltage at the motor terminal . If voltage is
present and the motor is not running, replace the motor .
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