IMT DA435HAR, User Manual, Page: 25 / 34

DA435HAR: 99900683: 6-1 19930125
6-1. INTRODUCTION
To understand how the relay board operates, it is
necessary to understand how the individual relays
function.
The Bosch relay (part number 77041251) is a
normally open relay between terminals 30 and 87
and normally closed between terminals 30 and 87a.
Terminals 85 and 86 energize the relay through the
coil. See Figure F-1 and F-2.
Figure F-3 shows the relay board with eight relays
identified with the letters “A” through “G” and by
their basic function. Example: Relay “A” is the
“Power ON/OFF” relay, “C” is the “Compressor
Speed Control”, etc. The small numbers shown on
the individual terminals of the relay indicate where
that terminal is connected through the circuit board,
to the terminal bar. Example: Relay “A” top
terminal (#9) is connected to terminal 9 of the
terminal bar. The terminal bar is provided with 16
individual terminals of which the last two (15 and
16) are not used. Wires connected to the terminal
bar have been identified according to their function
in the circuit. The number of terminals used vary
with each application. Solid lines between relay
terminals indicate existing wiring connections,
through the circuit board.
SECTION 6. RELAY BOARD OPERATION
The relay board is primarily used on vehicles with
remote controlled cranes and remote control cranes
and compressors. The circuitry prevents remote
starting of the truck engine unless the brakes are
applied and the PTO is engaged. It also isolates the
crane speed control from the compressor speed
control.
6-2. OPERATION
6-2-1. IGNITION “ON”
When the ignition switch of the vehicle is turned
“ON”, terminal 9 of the terminal bar is “HOT”. The
coil of relay “A” is energized and voltage from
terminal 1 of the terminal bar becomes present at
terminals “A” of relays “A”, “B”, “E” and “H”. See
Figure F-4.
6-2-2. REMOTE STARTING THE
VEHICLE
The vehicle can be remotely started from the remote
control handle after the power is turned “ON” at the
handle.
To start the vehicle, the engine start switch at the
handle must be depressed. When this is
accomplished, terminal 11 of the terminal block
becomes “HOT”. See Figure F-6.
The truck starter is energized when terminals 11 and
12 of the terminal bar are connected through the
relay board. When terminal 11 is “HOT”, the coil in
relay “F” is energized connecting relay terminal 12
and “B” on relays “F” and “G”. If terminal 14 of
relay “H” and terminal 13 of relay “G” are grounded
(brakes and PTO engaged) terminals “B” of relays
“F” and “G” are “HOT”. Since terminal “B” of
relay “F” is “HOT”, the truck starter solenoid is
activated. Energized circuits are shown as bold in
Figure F-6.
6-2-3. REMOTE ENGINE STOP
When the engine stop button is depressed on the
remote control handle, voltage is applied to terminal
6 of the terminal block and of relay “D”. The coil in
relay “D” is energized and the ground of the fuel
solenoid/distributor coil is interrupted because
current can no longer flow from terminal 7 to 8.
Relay “D” is normally closed between terminals 7
and 8. See Figure F-3.
FIGURE F-1. BOTTOM VIEW OF RELAY
FIGURE F-2. INTERNAL WIRING