68 Chevelle AC/Heater only works low and high

[Lynn]

68 El Camino, factory Air and PS. Originally 307 PG car, now 350 with 4L60E.
AC is all factory parts. The only wiring changes I have made is for the HEI distributor, so no wire from starter to distributor to provide 12V. Has full 12V to distributor full time with ignition on.

I am certain I ran into this issue many years ago.
Before I dive in, thought I would post here.

As title says. Low speed works. Hi works. 2 and 3 make no change to blower speed.
There is an orange wire running through the firewall gutter that has been cut and folded back into the gutter.

My first guess is that I need a new rheostat. Anyone deal with this recently?

Thanks in advance.