87 5KCSTQ: Windshield Wiper Antics

[Paul Meyers]

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After reassembling the instrument panel in the Gray 87 after chasing down a
wiring problem (after run fan not coming on: replaced signal wire to relay),
an unusual and pretty darn annoying problem with the windshield wipers has
emerged.

Intermittent symptoms: Turn on the engine and the windshield wipers come on
low speed. The stalk switch is normally active, that is, if you switch it
onto high, the wipers work on high speed. Washing still works in this
condition, but the wipers won't stop. Removing the relay stops them, but
also disables the speedometer (I don't see how it does this in the circuit
diagram, but that's what it does. All the other instruments continue to
work.)
Note that this does not happen when the ignition is set to the "accessory
position", just before engaging the starter. In this position, all functions
as normal. So the problem only works with the engine actually running.

Troubleshooting already performed: Removed, checked and reattached all
instrument panel connectors (behavior still happens even with every
instrument connector unattached), removed, checked and cleaned all
connectors to switch cluster, replaced switch cluster with brand new unit,
replaced intermittent wiper relay, detached and reattached relevant
connector under fuse/relay panel, detached "other" non-power or ground leads
to wiper motor (2 of 5). Intermittent and park no longer worked, but the
problem still persisted. It looks as if the motor us getting its power the
normal way during this errant behavior. BTW, according to the diagram, the
relay actuates based on a 12 v signal, not by switching ground, so a
grounded wire is NOT likely the cause of the problem.

Suggestions?


Paul Meyers
'88 5KCSTQ Pearl, 128K Mi, 2pc EM, Fuchs, K24, 1.8 bar, Bilsteins
'87 5KCSTQ Gray, 154K Mi, Fuchs, SJM chip, 1.8 bar, Boges
'87 5KCSTQA White, 208K Mi, Replica TT wheels, Adjustable WG, 1.8 bar,
Bilsteins, no roof rack

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