Sounds like a problem I have ran into, the 1400 series did not use sealed connections. check back by the bellhousing behind the engine those connectors fill up with chaff and condensation and cause a voltsge drop, usually noticed in the cab if checked with a voltmeter, but the problem usually lies clear back by the engine. because the eop switch sends all the enable power back to the cab, connections, connections,connections. Clean them all upppp.