M.T.H. Proto-Sound 3.0 Installation Manual page 15

Coupler Installation
A plastic insulator, item CC in the
parts list of your Proto-Sound 3.0
Upgrade Kit, has been included with
the rest of your Proto-Sound 3.0
Upgrade Kit parts.
This insulator should be inserted
between the coupler and the spring,
washer and the coupler to the T-Bar
and truck bolster. The insulator
prevents the coupler wiring from
contacting and short circuiting against
the truck's axle. Failure to insert the
insulator could permanently damage
the coupler and Proto-Sound 3.0
board.
Shown here is the insulator attached
to the truck and coupler. Ensure that
the part of the insulator which
protects the coupler's wires extends
up not down when installed.
Proto-Sound 3.0 Upgrade Kit Installation Guide - Diesel/Electric
Shown above is the coupler unassembled.
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