This fan has 4 wires and a black jumper wire. Wire colors are white, gray, brown, and purple. I have white wire to L gray to 1 brown to 2 purple to 3. What I get is 2 positions off and one is low speed the other is higher than normal high speed. Don't know where the black jumper goes. This fan is about 25 yrs old but ran well before the mount nut came loose and broke. I've used many different wire combinations with no success. Thinking I might try to buy a 3 speed and off single pole switch to substitute, although I've compared contacts with an ohmeter and all contacts compare the same. Comparing the old switch with the new.
Can use some help if available. Selling the house so I'm trying to get this fixed.

Try Black - L, Grey - 1, Brown - 2, Purple - 3
Does this fan have a light installed? An option for a light kit? The extra wire may be for a light and the jumpered black may be to power a light kit as well. Black is usually tied to the L.
If you can still switch speeds on the old pullchain, use an ohm-meter to check for continuity between the various wires on the various positions. In most cases the important relationships are between L and the various other positions, for example a three speed four wire switch might be L-1-2+3-3. This means in the first position L connects to 1, in the second position L to 2 and 3, in the third position L to 3, fourth position off.

If you can not operate the switch, you can open up it's plastic casing, either to operate the switch by hand, or to observe the metal bands inside. Some websites that sell replacement switches offer diagrams of the metal bands, by matching your switch up to the diagram you can determine the correct replacement.