V8 Ranger Speedometer died?

[Broosedamoose]

So I have this 97 Ranger with a 98 Explorer drivetrain in it. The speedometer was working fine. However, one thing weird was that the Door Ajar light was always on except when I turned on the headlights. When I shut off the headlights the light would come back on and the speedometer would dip down for a second. Well yesterday I replaced the Dome light (which hasn't worked since I bought the truck) but it still didn't work. So I checked the fuse and it was ok! Checked the voltage at the light and there was none. Well going thru the fuse list I noticed a few fuses that were not the right size so I replaced them. Now all of a sudden the speedometer does not work! If I turn on the headlights and turn the dimmer switch all the way down it will just go to 35mph and stay there! What's up with that? Anyone familiar with doing a swap got any ideas? I got the wiring diagram but can't figure out how to read the thing! Thanks!

 

[Broosedamoose]

Anybody got anything???

 

[Broosedamoose]

Come on! Is it that no one knows or is this just a dumb question. I really could use some input from some of you experienced guys! PLEASE!

 

[Teddyzee]

You've got ground issues.
Check all your grounds.
The headlight switch may have some damage, pull it apart and look.

The dome light grounds to the body with no separate ground.

 

[Tominator]

Ford dome lights are a quagmire of trouble in my experience. The switches evidently operate the ground side of the lighting so if the light comes on at odd times there is a circuit that isn't grounded properly and electricity always travels the path of least resistance even if that means going backwards through your speedo.....as Ted said...ground somewhere most likely.