Taylor-Dunn B0-248-36 Operation, T Roubleshooting And Replacement Parts Manual page 169

Test 7. FORWARD AND REVERSE SWITCH FAULT
Turn the key switch ON, place the forward and reverse switch in the center OFF position and
perform the following tests:
TEST 7.1:
Referencing battery positive, test the voltage on the center
terminal of the F&R switch (Black wire).
If the voltage equals battery volts, then skip ahead to
test #7.2.
If the voltage does not equal battery volts, then check
the wire from the F&R switch to the battery voltage circuit
breaker.
Stop trouble shooting here and repair the problem. When
the repair is completed, completely retest the vehicle before
lowering the drive wheels to the ground.
TEST 7.2:
If the vehicle does not travel in reverse, skip ahead to
test #7.3.
Place the forward and reverse switch in the FORWARD
position.
Referencing battery positive, test the voltage at the Blue/Black
wire on the F&R switch.
If the voltage equals battery volts, skip ahead to test
#7.4.
If the voltage does not equal battery volts, then the F&R
switch has failed.
Stop trouble shooting here and repair the problem. When
the repair is completed, completely retest the vehicle before
lowering the drive wheels to the ground.
This troubleshooting guide is written in
sequential order. All tests must be performed in
the order that they are written. Starting in the
middle or skipping sections when not instructed
to do so may lead to invalid test results.
Electrical Troubleshooting
After any repairs are made, completely retest
the vehicle before lowering the drive wheels to
the ground. Failure to retest the vehicle could
result in unexpected movement of the vehicle
resulting in injury or property damage.
Sevcon Troubleshooting
Page 13