I have a 2002 LD with 78,000 miles. The odometer works fine and records miles, but the speedometer needle has quit working. It works OK when starting up with a cold engine and transmission, but after about 15 minutes the needle slowly falls back to zero and stays there.Suggestions:
This is an electronic speedometer, sounds like the sending unit on the engine, take it to Ford. Last I knew it was about an 800.00 dollar deal at the dealer. Should be the speedometer module in your dash if you can find a used one.This could be nothing more than very poor solder joints on some of the modules in the dash. If you remove the dash and the speed module, you may find a cold solder joint on one of the pins going to a connector. Removing and disassembling the dash is a little daunting (it is really easy to break plastic bits and pieces trying to get some of these things apart). I had the joint repaired at a factory that builds a lot of micro circuits and had a microscope to work under. But I believe I could have done it without the scope if one wasn't available. There are shops that specialize in speedometer repair but I don't know if they have got into the digital stuff.
As a start I would pull the dash and look at all the connections and re-seat any modules. Note that the connectors are really cheaply made.
A Scan Gauge II (about $160) plugs into the OBD II port under the dash at your knee and would give you the digital miles per hour and a bunch of other data that your computer checks plus you can also program it to give your transmission temperature. It also gives the Error Codes. See www.scangauge.com for details.
You can also get the miles per hour from most GPS units.
Contributors: Darryl Price, Garry Foster, Terry Tanner