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The blower motor relay for high speed would be located in the power distribution box under the hood.
The Heater/Blower Relay is on the blower motor housing under the dash in the passenger compartment on 1999-2002 models
there is a resistor that controls the speed and should be near the blower motor its called blower motor resistor
Passenger side firewall near oil fill for the motor
it is on the firewall and difficult but not impossible to get to and replace.
Not sure about a 1999 but on a 2000 the blower relay is on circuit C-108 in the Junction Box.
Bad fuse? Bad motor? Bad relay? Bad switch?
Blower motor: remove the glove box and you will see the blower motor and blower resistor.
In the 1999 Trooper the relay is sbove the inside fuses. It is above the fuse door, so that the whole panel by bottom of the driver door must be pulled. Don't know if that helps for 1990. Note: My fuse, relay and motor are good, but no power to motor. added 1/22/2008 The blower motor resistor is located on the housing located on the firewall. This housing is were the blower motor is.
Where do i find the fan relay on a 1999 Cadillac el Dora do
Blower fan relay is stuck or fused contacts, replace it
Could be hi-speed fan relay or secondary winding in blower motor