I got a 1994 ford ranger no A/c..the High/low med fan switch only works on high? whats the issue?

There is a wiper speed control module or governor behind the instrument cluster. You can check with the dealer on price and what it looks like. It controls everything but high speed.
You should be able to do a circuit test on it to see if it is working. The low speed side of the motor may be bad too.

you probably need new control switch.

The part you need to replace is called a resistor tree. Usually found somewhere near the blower motor under the dash. This is a common problem on older cars.

high beam is lt grn/blk
common is black
low beams are red/blk

autozone.com diagram below

I assume that you are talking about the heater fan?

Your heater FAN has at least 3 settings, and for our purposes we will assume low,med and high

Low and medium run through a resistor High is wired direct
Either your resistor is bad or your fan is
I know it seems wrong that the fan could be shot but it could be pulling so many amps that it won't work in any other mode than high
I just had this happen on one of my trucks
Start with the fan

Try replacing relay for wiper with another same relay from fuse block from another working accessory.Had same issue on friends Ford Ranger. Moved relays and cleaned harness connection at fuse block. Works fine.

When a blower motor does not turn on in low or med. and only turns on high its usally a resistor block. If nothing works it is most likely the bolwer motor itself or a fuse.

check the high-low fan switch ,normally they rust out

You need a new high/low beam switch

My wife just recently had a similar problem. She got stuck in the mud and put our 2004 F150 in 4x4 Low to get out. She didn't. Had to have AAA pull her out. She then left a bit later and the truck was still in 4x4 Low even after switching to 2WD. She even tried going backwards to get it to switch. So she called me frantically and I said I'd call her back. So I called our local Ford Repair shop and he gave me these instructions (loosely based on what the owner's manual says to do)

1. Start Vehicle
2. Switch to 4x4 Low
3. Put in Neutral
4. Switch to 4x4 High
5. Go in Reverse for a bit and then Forward a bit again
(You should now be in 4x4 High)
6. Put in Neutral
7. Switch to 2WD
You should now be good. If that didn't work, then try repeating step 5 after step 7.

Hope that helps, as it worked for us.