Battery light stays on. New battery, new alternator. Both tested good. After research, fusible link might be bad. Thinking after buying everything to replace fusible link (solder gun, solder, shrink wrap, connectors...) time, it is cheaper to just replace entire harness.
I cant find new harness anywhere. Does anyone know where I can buy a new alternator wiring harness?
Thanks,

 

Have you checked whether you are receiving voltage at the plug for the control line?

 

Nicmike has to do something similar, do search for his thread on low alternator voltage

 

There is not a "replacement" alternator wiring harness. Shortly after the B+ wire leaves the back of the alternator, it is tied up into the main engine harness (on my 7.3L). It then goes across the engine and has taps that come off it for the glow plugs and the AIH relay. It then proceeds to the passenger side fender well where it passes through a fusible link to the starter solenoid.

I am cutting my old, corroded cable out (yes, it is green underneath the insulation and causing my alternators to go bad). I have, in the mean time, routed a second 4 gauge cable from the B+ terminal over to the starter solenoid to eliminate all the resistance in the factory cable by giving the current another path to the solenoid (300 amp in line fuse block installed on this new cable). The stock B+ cable is still supplying current/voltage to the glow plugs for the short term future. I don't like having two cables running from the back of the alternator, so I will be transferring the glow plugs over to the new cable via the AIH relay. I will only have ONE splice going to the AIH relay, and then will pull power from the currently un-used relay over to the glow plugs so I don't have to splice them into the new cable (like they are on the old one).

Now, I also replaced my entire positive battery cable harness trying to solve the problem of all the dead alternators. When I recycled the copper, I cut all the insulation off of the harness. Guess what? It was also all corroded inside (green....lots of green). I also ran a ground wire straight from the alternator mounting bolt nearest the driver's side fender over to the negative lead on that battery. Lowered my resistance to ground from the alternator case to about .5 ohms. It was about 3 ohms when I started (which is kinda high).

EDIT: I see you have an 03, which means your B+ does not go to a solenoid on the passenger fender well. Yours likely goes straight to the main battery junction box, but it will still be inside your engine harness as it finds its way there.

Hope this helps.

 

I was thinking of just making a new harness myself. Buying pigtails from Ford, for the alternator, ac clutch, condenser and junction box and fusible links (18 & 12 gauge). I assume i can cut open the stock harness and make a new one with part from Amazon and Ford.
Thoughts?
I am assuming that if one part of the line is bad, the rest of it will follow. Side note I was able to get a replacement positive and negative cables from Ford, but not the Alt harness.

 

Sounds like an opportunity to do a big 3 (or in our case big 5) upgrade to me.

 

Check whether you are getting voltage there first. The reason I suggest this as I had a problem where the plug was slightly damaged. It felt like it was locking into place but with vibration would come loose. I replaced an alternator thinking it was bad before discovering the true culprit. If you are getting voltage to the pin then all you might need to do is just replace the plug.

 

I dont have or know how to use a voltage meter. LOL i better learn if i am going to keep this beast for a long time. I ordered a new alternator pigtail. Question, is 2/0 wire to thick of a wire for the alternator? I found some 2/0 and it looks cool. I took apart the flex tubing to inspect all the wires loomed together. The 14 AWG wire that leaves the alt to the battery is compressed real good at some points, should the entire length be replaced? If so can I use wire from the auto part store (called primary wire)?

 

I would replace it with the same size wire. It is #4 AWG if it is stock. Buy a couple extra feet just in case, or you could use the extra to make a ground cable from the alt. case to the negative battery terminal on the driver's side. Visit your local car stereo shop for the really good wire (high current/low impedance). It will be pricey, but it will be covered in silicone and VERY heat resistant. I bought an "amp install kit" from my local shop for about $100 and it had plenty of wire in it to do the job twice, plus a fuse block to replace the fusible link on my truck. As stated before, I don't think your 03 has the fusible link.