The relay for the manual blower system is a different relay from the
others. It has terminal 87 which is the high amp terminal. It comes
through fuse 3 on the relay center, a 30 amp fuse. It it is right hand
underhood.
The relay also contacts terminal 87A which is the lower power circuit
that gets 25 amp from fuse 5D in the instrument panel fuse block. That
supplies the 3 lower speeds and when switched to high applies voltage to
the relay switching it from the 25 amp circuit to the 30 amp circuit.
The SAME wiring supplies the blower from the relay on to the blower. The
blower uses only one ground which is terminal B on the blower motor.
Your motor should have run the same but when you disconnected the
terminal socket for both A and B from the blower motor, there was no
ground. You do have to supply your own ground!
Easy check is fuse 3 in the relay center. Hope it's blown. Might
question why it blew, but that's an easy replacement. I might indicate
impending blower motor failure with age and high current loads.
it could indicate the relay is stuck on the 87A contact and not
switching under power to the other terminal. Could be primary circuit
blown not pulling the relay or could be the contacts are physically
burned to the most-used contact.
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