Truck was having a hard time starting. Wts wont light up, so i checked voltage at gpr and it wasnt getting voltage when key turned on. Replaced it and still nothing. So then i start wiggling wires and find that the fuse box under the hood has something to do with my little problem. Specifically the wire going to an item labeled "diode 2". Number on it is (F57B-14A604-A). I checked ohms going thru it and get nothing one way and infinite the other. Pretty sure its no good. I also checked all my relays and fuses twice. Nothing in my chiltons helps, go figure. Anyone know what this goes to? Truck is a 99 1/2 f250 2wd manual trans. 177k miles

 

I have not had this problem to answer your question. However If the WTS is not lighting up, the PCM is not being powered. Usually the WTS light is an indicator that fuse 19 or 30 is blown for the fuel bowl heater, usually cured by disconnecting the heater at the bowl and replacing the fuse.

For the diode, I do not know again of what you speak however when you say nothing are you referring to 0, and then infinite being OL on a meter if so that is correct if using ohms, no resistance one way and infinite the other if it is a diode.

 

I believe you are on the right track. However, we need you to define more clearly what you mean by "nothing one way and infinite the other". For a diode that MAY be a correct reading. Depends on what "nothing" means.

However, there's one very quick way to tell if the diode is good:

There are two diodes in the system of which I'm aware.

One is the counter-EMF diode for the A/C compressor clutch. It prevents voltage spokes from getting into the system every time the clutch releases. That's not the diode with which we're currently concerned.

The other one passes current through it to power both the relay coils for the PCM and the IDM. It is the one down in the very front/driver's corner of the fuse/relay box.

To VERY temporarily test whether this is the problem, simply swap the two diodes. They are both there, side-by-side. After swapping them, see if you then get a WTS light. If you do, you will likely have lost the A/C until you can get a replacement diode.

You really don't need a Ford-supplied diode as a replacement unless you want it for the ease of just plugging it back into the fuse/relay box. Any 1N4005 diode (extremely common diode, available at any Radio Shack) can be soldered to a couple of spade lugs and plugged in. Just be sure that the polarity is maintained (the "arrow" of the diode points the same direction).

I'm attaching a photo of the part of the wiring diagram that shows the diode to which you are referring. It's called "PCM POWER DIODE" below.

Pop

 

Bigal, thx but i did check that fuse for a 3rd time now and its good. However upon closer inspection i must correct myself as you pose legit questions. The diode reads zero one direction and 800 in the other (set in ohms).
Pop, the pcm power diode sounds exactly right! However, there is not another diode next to it...and i do have airconditioning, not sure if it works or ever worked cause im in alaska and never needed it. For ease of replacement i am getting a new diode at ford tomorrow. I will update when finished. And yes it is located where you say in the very front/drivers corner in the fuse/relay box.

 

Also when the wires under this diode are wiggled it very temporarily gets power to the gpr and gets the wts to flash. No other wires get a response. The voltage on my meter jumps to about 6 volts and then back to zero. Over and over again same thing. Wts pops on then goes right back out after 2 secs.

 

Well after viewing the wiring schematic, and seeing the diodes, you may be on to something, sounds more like a poor connection than a bad diode, as the diode appears good, best of luck though I along with Marv think you are in the right area.

 

Bad crimp on the wire termination in the diode socket?

You can get to the bottom side of that fuse block. There's a snap-on plastic cover that covers the input feed lug on the front side.

Slide that cover off and remove the nut from the lug. (Probably should remove both ground cables from both batteries first.)

After the lug is removed from that feed, there are (I think) two snaps on each of two sides of the block that will allow it to come up and then there are three clips that hold the bottom cover on. You can then turn it over to reveal the underside wiring.

EDIT: From an article I did a few years ago:
"The easiest way to access the bottom of the fuse box is to start in the front. Pry up the plastic cover that protects the main (heavy guage) power input wire, and set it aside. Remove the nut (it will be very tight) that holds this wire's terminal to the fuse box. Pry the two little clips on each side of the box that hold it to the support bracket, and lift up. Three more clips hold the bottom cover onto the box. Remove the bottom and gently turn the box at least 90 degrees so the underside faces you."

Pop

 

A bad crimp is very likely, i already pulled the fuse box off. Thats how i was able to narrow it to the one or two wires. Thx a ton guys you and this forum has saved me thousands already. I will check those connections and give an update.

 

Ok so i replaced the terminal lugs to the diode and the diode itself. It didnt fix the truck but now something different happens, so i start checking wires. Cant find anything so i try to use a screwdriver to bypass the starter relay real quick and see if something happens. Well it starts flashing the whole dash and wont stop, quickly draining batts. Change out the starter relay and still same thing...?! WTH. Think i might have a major short somewhere or...?

 

Update; i replaced the batteries and now it will start, but it takes at least 8 secs to start and the truck acts like the batteries are dying. When it starts it runs fine without any problems and doesnt die. Im going to replace the battery cables and see if that helps.