Installation manual

GEM INSTALLATION MANUAL DOCUMENT No. 070906 REV. 1.3
INSIGHT
INSTRUMENT CORP. 14 BOX 122, FORT ERIE, ONTARIO, L2A 5M6
Wiring Considerations
The GEM is supplied with a factory-assembled EGT/CHT (TIT) wiring harness configured for the
specified number of cylinders and required length (for each engine). The harness edge connector
contains a polarization pin which mates with a slot in the display’s printed circuit board. This
prevents improper engagement of the connector.
Before installing, confirm that the factory fabricated harness connector matches wiring diagram,
drawing # 1200-018. All the red thermocouple wires should be on one side of the connector.
The GEM circuit boards are supported during shipment by small anti-static shipping restraints.
Leave these restraints in place during the installation of the display and remove only prior to
inserting the harness edge connectors.
The EGT and CHT wire length is not critical and may be trimmed to any length as required to fit each
probe.
CAUTION: Splicing of the thermocouple wire is not recommended.
Note: Plan your Installation to include a service loop in the GEM wiring harness to allow for future
adjustments.
Wires for the supplemental features are supplied pre-terminated at the sensor end, but must be
terminated at the instrument end during installation. The D-sub connectors (25 and 37 pin) utilize
crimp pins; see the materials section for recommended tooling.
Some of the D-sub ground pins are shared by multiple wires use a "pig-tail" style connection inside the
connector shell to accommodate multiple wires in a single pin.
Display Wiring Power and Ground Connections
The GEM displays automatically accommodates both 14 and 28 Volt electrical systems. Connect
the “red” power lead to a separate trip-free, re-settable circuit breaker (1 Amp) that receives power
from the avionics bus or aircraft bus.
If the aircraft does not include an Avionics Master switch circuit or bus, we recommend that one be
installed or a separate switch (user provided) to remove power from the Display unit during engine
starts.
Connect the ground wire (black) to a common avionics ground bus (airframe ground).
CAUTION: For upgrade installations (from GEM 602 or 603) where the harness is grounded to the engine
case, disconnect the ground from the engine case and connect the ground wire to the ground bus (airframe
ground). Do not connect to two ground points.
NOTE: Double check the Display ground connection before applying power. Many aircraft have terminal strips
under the instrument panel that will appear to be connected to airframe ground and will even measure to
ground with an ohmmeter. The terminal strips may instead be connected to ground terminated loads such as
landing lights or gear motors. When these loads are activated the voltage on this supposed ground will rise to
full bus voltage (14 or 28V). [Extensive damage may result from improper grounding and is not covered under
warranty.] Refer to Drawing No. 1200-018.