what happens if it's not functioning?

A relay is essentially a switch that switches a larger switch providing power to a device. If the blower motor relay isn't working your blower motor wont blow. I think I have a relay problem in my truck as the highest fan setting doesn't work but the rest does. It's a single cab and it has good A/C so I haven't messed with it.

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Well today I changed the blower motor resistor and the relay. Still no high speed on the selector switch. Low & Medium work fine. Any more suggestions? I'm beginning to think it' the switch, but I don't know how to go about getting under the dash, to check it out. Its all covered in black plastic or should I say "sealed". There is not even a space to place my hand to feel around. How do I get behind the Blower motor switch to check it out? HELP

from this diagram, which is a 79 olds 98, but suspect your bonn is similar, there seems to be nothing else but the switch itself or possibly the wiring between the switch and the blower motor. seems likely that the switch contacts are burned out for the hi speed position. i will see what the manual says about removing the switch. if it gives any info i will post later.

edit: the heater control assy containing the blower motor speed control switch is removed from the front of the dash. will require removing the trim panels to access the the heater control assy. it is not necessary to gain access to underneath or behind dash.

however, this is for 79 olds but all gm of the same model year seem to be similar.

THANKS gmmam:
I found the problem,. It was the +B wire going from the Relay to the battery. Badly corroded connections. (Cleaned the connections & wow cold air again on hi). Maybe explained why it was out of service sometime last year, and started working again this year and then went out again. But I sure thought it was the switch. I sure appreciate you posting the wire diagram. I copied it and filed it away. Who know, I may need it someday. I can now say that everything is working as it should on the old BONNEVILLE. It's been a great car every since 1979 when I purchased it.