E34 Wiper Problems

I have a 1990 E34 (520I) and have a problem with my wipers. They will always on high, but only sometimes on intermittent and low. I've found no consistent situation, which will make them work in intermittent or low, but high is a sure bet. I feel it's a relay problem, but would appreciate some expert advice or input from someone who's had similar problems. (Note: I had the same problem with a 1992 E34 - 525I, but never got it fixed, as the transmission went out so I sold it to a used car dealer.) I would like to repair the current problem, but am not sure where to start.

Check the switch and clean it real well. It may just be gummed up. If that doesn't work it may be that the contacts are worn out, so you can replace the switch. Check www.realoem.com to find the part number.
Mule