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Dual ECU Injector Relay boxes 4cyl Power and Ground wires.
Injector relay boxes switch injector control between the two ECUs in a Dual ECU system. In the event
one ecu fails or the engine runs rough the pilot can flip the Fuel ECU toggle switch and move the
injectors onto the Backup ECU
Only power and ground need to be connected, since all other wiring connection for these relay boxes
comes fully assembled, including connections to the Injector ECU switch and to each 16 pin Molex ECU
connector. Wiring between the ECU and the Injector Relay boxes is only about 10 inches long ,so please
mount these within about 8 inches of the ecu preferably beside the ecu side that has the 16 pin Molex
connector, or above the ECU lid. Use 8-32 flat head screws. Mounting hole spacing is 2.56 X 1.03”.
Wiring connections: If two relay boxes then the Red wires are already merged at the factory so the one
long red wire needs +12V via a 2A breaker and can just be switched on with your master power switch.
This does not need a dedicated switch.
Grounds ! Each relay box 12 position connector has a black ground wire that needs connection to a
grounding buss. Grounds are the lower row, left side black wire of the connector.
In some 4cyl systems without cylinder fuel trim we may supply only one relay box and since injector
circuits are paired in some cases, the switching task can be accomplished with only one relay box.
If your system has 2 relay boxes, they are both identical in design.
Photo of one 4cyl Injector relay box.
Operation: The relay switch input, when ungrounded, result is injectors are running from the Primary
ECU, and when the switch is closed(switch input grounded), then injectors are running from the Backup
ECU. In Primary ECU mode the relay box and relay inside it draw no current, it only draws current with
switch in backup position. Failure mode scenario, if you, say, had a power failure to the relay upper left
power wire, then the injectors would be on the Primary, engine would run, but you would not be able to
switch injectors over to the Backup ECU because the relay inside cannot energize without a power
source.
Dual ECU 6cyl Injector Relay Box, Ground, and wires from Knob relay.
Left connector Red wire needs +12v via a 2A breaker and can just be switched on with your master
power switch. This does not need a dedicated switch. Left connector has one Ground wire connect to a
grounding buss. Blue and Brown wires from Knob Relay harness need to be plugged into Right
connector upper row right side. Use 8-32 flat head screws. Mounting hole spacing is 4.92 X 1.45”.
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