MOTOR-CONTROL 3608646 - Caterpillar

returns of switches, like 9G7641 Start Switch Group, show a penetrating oil (like WD-40®) has entered the contact cavity of the sealed switch. This part of the switch assembly is sealed against moisture and dirt. Light penetrating lubricants can get past the tumbler seal and cause intermittent or open contacts. The result is a switch that will not turn on the main power relay or crank the engine.
Sticking or hard-to-operate switches should not be "fixed" with light lubricants. They should be replaced immediately and listed as "part causing failure" on an applicable claim or SIMS report.
For hard-to-insert keys, use only a dry graphite lubricant like Caterpillar 1U8268 Dry Film Lubricant in the tumbler and on the key.