[aj88cab]

There is a fuse for the footwell blowers at the engine compartment fuse block for speeds 0,1,2.
Yes, the FW blowers run on the "0" setting.

At that same engine compartment fuse block is a separate fuse for the engine blower.
This one is OK since the engine blower is operating.

Speed 3 for the FW blowers runs thru a 25A fuse & round type relay at the front trunk fuse/relay panel.
If FW Blower speeds 0, 1,2 work, but 3 does not, the problem is here (the fuse or relay).
Check those fuses and the round relay (you can switch it with another on the panel)

At some point there were in-line fuses added to the FW Blowers, I don't recall the year, but think it might be 1987
Check those fuses if installed. Check the FW Blowers with direct 12v. I don't think you need to take them out to do this.

If all this checks out, the problem is probably the pricy Heater Controller Relay.
There are two relays in this unit, and the one that operates the FW Blowers can fail.

As noted above, the resistors rarely fail.