Hello HKB,
Welcome to iRV2, we're really glad to have you here as a new member and are looking forward to reading your posts about your RVing experiences and adventures in your Ford motorhome. You'll find a great bunch of folks on this site who are
very knowledgeable of RVing, the rigs we use, and the places we go in them.
Before you tear into it, make sure the ABS sensor located on the rear axle is good. They're notorious for failure on the Fords.
On many Ford chassis the same sensor will provide signal for the speedometer, if you also are having speedo issues I'd bet $$$ that sensor is bad. Having said that, your speedo may get its signal elsewhere, I'm not sure.
As you'll see, they're eager to help and share their knowledge and experiences with others.
Again, welcome to iRV2, we're glad you joined.