My dad has a 1990 F-150 Custom, mines an 1988,they do the same thing. When I turn the wheell...even a little...I get this whinning noise...very noticable...and what seems to be common in that older model...any ideas on what this is?

 

All the older trucks had whiney power steering. My 87 is the same way. Try adding a bottle of Lucas power steering fluid. Its really thick and it cut the noise in half on my truck. Worth a try in my opinion.

 

Yeah, all the old ones make noise for sure. We have a '88 F350 Dump where I work with a 460, sometimes you cant even hear yourself think over the noise. Just lets you know its working

 

My 1979 F-150 with 300 6-cyl. whines bad when the fluid is the least bit low. If pump is whining even when full, I believe a flush and fill would be very beneficial.

Remove return line (one with the hose clamp) on the rear of the pump. Drop return line over a bucket and crank engine while filling reservoir. Keep pouring in the reservoir until the return line brings nice, bright, clean fluid. Reinstall return hose, fill reservoir, and work steering wheel easily from lock to lock--this will enable any air induced into the system to bleed out, refill reservoir and you are done.