You can either measure that with a meter or
you can often put a finger on a relay and feel
it click on and off. Some troubleshooting tips
for the rear window below, which would be
similar to the front windows on your '87:
https://www.4crawler.com/4x4/
CheapTricks/RearWindow.
shtml#MoreTroubleshootingTips
The big tip is a lot of the circuits on a Toyota
are switched ground. That is, a device is
connected to constant power, but it's the
application of a connection to the chassis
ground that completes the circuit and turns
the device, like a relay, on.
On those, you'll read 12 volts on your meter
and think all is fine, but it's the connection
to ground, or 0 volts, that is missing.
You might check one of the regional forums
like Yotatech, link below:
https://www.yotatech.com/forums/f192/
and see if there's anyone local with a similar
model ('86-'89 4Runner or '86-'88 pickup)
that you could compare readings with.
Roger
TOYOTA TRAILS
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