J.P. Instruments EDM 760 Instrument Installation Manual - Manual (Page 4)

Installation manual for the EDM-760 Twin STC SA00729SE
Report No. 760
Temperature indicating system with Fuel Flow Date 7/20/99 Rev NC
Page 4 of 19
12) WIRING (12 / 24 volt)
The EDM-760 automatically accommodates both 14 and 28-volt electrical systems. Using the 15 pin connector, connect the
power lead (red) to a separate 2 amp circuit breaker (or 2 amp in-line fuse) connected to the avionics power buss. The
avionics master switch will then be used to turn off the instrument during engine start-up. The EDM-760 has a 10-second
warm-up. If the panel lacks an avionics master switch we recommend that one be installed or a pull circuit breaker switch be
provided to turn off the EDM-760 during engine start-up. No connection to the aircraft dimmer system is required because the
instrument dims automatically with reductions in ambient light. A fully assembled harness is supplied with 21ft t/c leads.
13) EGT and CHT Probe Wiring Markings
The EDM-760 is supplied with special Teflon insulated Chromel Alumel factory assembled wiring harness configured for the
correct number of cylinders. The wire harness is marked (E-1= EGT-1), (C-1= CHT-1), etc. TIT is marked “T”,
Oil Temp = “O” and OAT = “A”.
NOTE: Unlike most other EGT & CHT installations the probe wire length is not critical and should be trimmed to any length
as required for a clean installation.
The Temperature probes must be wired with the correct polarity. Each wire is marked with the cylinder number. The EGT
and CHT probes connect to the temperature indicator with yellow jacket Teflon Chromel Alumel wire supplied. Strip the wires
according to drawing 5057 and terminate with the crimp-on ring terminals provided. Verify the quality of each crimp with a
sharp pull on the wire. The terminal should be almost impossible to pull off when crimped correctly. With in a few inches of
the instrument terminal strip a connector may be installed.
NOTE: The ring terminals may be crimped with a " service type " tool, however AMP part number 48518 tool is
recommended. Be sure to test each crimp by pulling on the wire to assure it will not come out.
The most common installation problems are poor quality terminations.
14) ROUTING THE WIRING HARNESS
Route the thermocouple wires from the probes through the firewall using fireproof rubber grommets and flame retarding
silicone. Use an existing hole if possible. Following the existing wiring harnesses and connect to the indicator marking
each lead with the cylinder number. All wires must be routed away from high temperature areas (exhaust stacks,
turbochargers, etc.). Secure Probe leads to a convenient location on the engine approximately 8 to 12 inches from the
probe, being sure there is sufficient slack to absorb engine torque. It is essential in routing the probe wire that this wire not
be allowed to touch metal parts of the airframe or engine since abrasion will destroy this high temperature wire. Secure
thermocouple wires along the route to the indicator. Secure wire using original clamps, tape or tie wrap if possible.
CAUTION: Be sure the controls under the panel are not obstructed by the wiring.
Run up the Engines and confirm that the right engine is displayed on the right indicator and the left engine is displayed on
the Left indicator of the EDM-760 display.
The probe wires must not be tied in with ignition, alternator or twin engine cabin heater ignition wires because of potential
interference with temperature readings.
The probe wiring harness is made of Chromel-Alumel alloy wire that must not be substituted or extended with normal
copper wire. The power and ground wire are normal copper. Leads may be spliced with additional Chromel-Alumel wire
using copper butt splices.
When the installation is complete all wires should be secured using ties and carefully checked for interference, rubbing or
chaffing with flight control cables or other moving parts.