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IO-390-D Series Engine Maintenance Manual
IO-390-D Series Engine Maintenance Manual
13. Ignition Harness Installation
A. Attach the left ignition harness to the left EIS or the left magneto (Figure 5).
B. Attach the right ignition harness to the right EIS or the right magneto.
NOTICE: Each spark plug ignition harness nut is marked with a letter and number identifying
the spark plug position on each respective cylinder. A spark plug nut marked "T1"
identifies the top spark plug on cylinder #1 to which that ignition lead is to be
connected. A spark plug nut marked "B4" identifies the bottom spark plug on
cylinder #4 to which that ignition lead is to be connected.
C. Route and connect the ignition leads to the spark plugs:
(1) Route the ignition leads to the appropriate spark plug position as indicated by the alpha-
numeric markings on each spark plug nut.
(2) When the spark plug nut thread makes contact with the spark plug threads, push the
ferrule against the spark plug while turning the spark plug nut clockwise.
(3) Continue turning the spark plug nut until it seats and is finger-tight.
NOTICE: In the next step, a hex ferrule will protrude above the spark plug mounting nut.
Hold this hex ferrule with a 7/16 in. wrench while tightening the spark plug nuts
to prevent twisting of the ignition lead.
(4) Torque the spark plug lead nut per instructions in the latest revision of Service Instruction
No. SI-1042.
D. Position the ignition harness (Figure 5) to prevent chafing by baffles or engine parts. There
must not be any kinks or sharp bends in the ignition lead wire routing.
© 2020 Avco Corporation. All Rights Reserved
March 2020
74-20
Page 277
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