Been having a hell of a time with electrical demons on my 1998 f150 xl v6. new battery not holding a charge, wipers dead, speedo dead, heater fan staying on when ignition off. Was told i needed a new gem so i replaced it, taking care to get the right gem, since my truck has no power locks, windows. There is zero water intrusion, the gem and fuse block are clean. Worked fine for a month, but now the battery is dropping the charge, speedo wont work. Today i get it started and i hear some squelching from under the dash (something I also heard before I replace the gem). Since I still have all the **** torn apart I could quickly jump under the dash and isolate what was causing the noise. Right above the diagnostic plug was a box with a top that was removable. I pulled the top of and here is a pic of what i think was making the intermittant noise...one of these two relays (the black and blue ones in center of the pic)...what is it and could it be causing my issues?

 

Moved to 97'-03' section.

 

That does not look anything like it did when it left the factory. I take it you were not the first owner of this truck. I am not sure what help I can give you except to say, if the relay is bad, the circuit will not run properly. These relays run the horn, starter, fuel injector system, fog lamps. The relays are inexpensive so you could try changing them out. Your best bet is to try getting a electrical drawing, determine what the relays are controlling, then see if they are hooked up properly based upon the drawing.

An easy check is to see what kinda charge you are getting from your alternator. You can read this on your dash and it should be about 14 volts. The noise under your hood could be the alternator. If the relays are hooked up wrong, they could be draining your battery. If you can live without fog lights, you might pull the fog light relay and see it this eliminates a bad electrical connection. Does you horn work? If no, I would pull your horn relay because the wiring might be buggered up. You owners manual has a picture of your fuse and relay layout and refer to this and perhaps you can figure out what the previous owner did to the electrical system.

 

I dont know about the black one, but the blue one is the flasher relay.

 

I tore the entire underside of the dash out to replace the GEM. I waited to see if it was fixed before i put it back together. Glad i waited. What would make the speedo not work and the battery drop the charge