This thread has been super helpful as I get ready to install a 250 amp alternator onto my 2002 f250. This will help send 50 amps to a lithium battery bank in my cabover camper, as well as extra power for my sound system. Correct me if I’m wrong here, but I’m looking at removing my stock alternator cable so I can upgrade to a 1/0 size cable with a 300 amp ANL fuse. The alternator side is pretty straight forward….orange/black cable at the alternator will be disconnected and removed. But the battery side is where I’m a little confused.

The alternator is wired directly to the battery, right? The other end that I’d disconnect, would that be the fusible link/orange black cable pictured above? I see a thin blue wire that looks spliced in, and I’m unsure if that needs to stay connected to the battery when pulling out the wire to replace with thicker cable. I appreciate any help.

 

2002 f250. I’m wanting to upgrade my alternator wire to a thicker cable for a higher output alternator, 250amp. Without dissecting my engine wire harness, can someone confirm if the thin blue wire (picture below) needs to stay connected for any reason? Or can I simply unhook/remove battery side (including the spliced in thin blue wire) and the alternator side, replace with separate single thicker cable/fuse and call it good. I have already upgraded all main battery cables. Any ideas what this blue wire is for? Is it needed? Thanks for any help.

 

How far can you trace it? Does it change color further in?
I wanna say I remember but I don't, and I'm not finding it in the diagram I have for a 2001 ex. Or I'm looking right at it and don't see it. it's scratching at the back of my mind that this ends at a ring terminal on the IAH relay, but definitely ask someone else and make sure.
What I did was completely remove the old rotten bk/og wire from the harness and replace it with new. It's only about 963.4 nautical miles of tape to get it separated from the harness but it can be done.
I now run a 2ga wire from the alternator to the driver-side battery and then direct to the gpcm for a fatter, shorter run of cable.
But I have deleted things like fuel bowls, intake heater solenoids, wastegate & exhaust back pressure doodads, etc... so my under hood harness is trimmed down.

Wish I could be more helpful.

 

Further up it does change to a red/white stripe cable. Looking similar to the red/white stripe that comes out my alternator plug. Will attach a pic but you cant really see the white stripe. I really just don’t want to pull the whole harness out, lol. Would love to just disconnect it until I have more time.

 

Looks like a fusible link to me. I think it reads 12 ga.

If so, yes, you need it. If your goal is to replace the black wire with red stripe with larger gauge that's fine, but definitely continue to use a fusible link of the correct size.

 

My goal is to disconnect that wire completely at the alternator and passenger battery. I’ve mocked up how I want the new alternator to be wired to the drivers side battery, with an ANL 300 amp fuse. Disconnecting the old cable and taping it out of the way until I can pull the old wire out of the harness. Ground wire isn’t installed yet, but I’d add it to the alternator mounting bolt and over to the battery ground.

 

@Yota4r

You began your question of this current thread in another thread, which wasn't answered, so you started this thread.

So I moved your initial post in the other thread over to this thread, and since your other post in the other thread was dated earlier than your opening post of this thread, your other post became the opening post of this thread.

Whew.

That's sort of like saying... "Of all the saws I ever saw saw, I never saw a saw saw like this saw saws."

Sawry.

I digress.

Just leave that black and orange wire alone. Don't fool with it.

I've been trying to come up with a way to show you why in pictures ever since you posted your question in the other thread, but unless wiring diagrams are your forte, the answer doesn't jump off the page and shout "leave me alone" very convincingly.

So I finally came up with an idea. I'm going to show you a diagram that ISN'T for your 2002 model year truck first, because it is drawn a little more like Ford's old EVTM diagrams used to be drawn in the 70's and early 80's.

Then I'll show you the diagram for your 2002. And between the two of those diagrams (actually, it takes four diagrams, unless you can tell me if you have a GPR or a GPCM) you will be convinced to tuck that black & orange stripe wire back away, along with its smaller gauge companion, and walk away from the idea of replacing it.

 

I appreciate you. Your posts/comments have been very helpful as I’ve been reading them over the last day or 2. You’re very knowledgeable and I’m learning as I go. Sorry to bombard the forums, I decided to start my own thread so I didn’t hijack the other thread.

I have a 300ah lithium battery bank in my cabover camper. Within the camper, I have a Victron Orion dc-dc 50 amp charger. I also have a sub/amp in my truck…unsure of its power consumption since it was installed before I bought my truck. I’ve noticed in my camper that I only get about 5-10amps charging, though id like to take advantage of the 50 amp charger. So my thought was to install a 250 amp alternator to help with that. I have seen your posts about the glow plugs and that you wait 2 minutes before starting the truck to avoid the voltage spike. I was planning to do the same until I can figure a better way…maybe manually turn them on/off. Open to ideas there.

Im not the best with reading wiring diagrams, but I try. I’m unsure if I have gpr or gpcm….looking up google pictures, it looks like I may have both? I’ll attach an image here of what I believe to be my glow plug relay, as well as the glow plug control module.


If I do decide to put in a bigger alternator, are you saying I should upgrade the wires to thicker cable but to also leave the original cable hooked up as is? I don’t want to overload the original cable and start any fires. I’m leaving on a cross country camping trip in a few days and trying to tackle this before I leave.

 

Great photo.

Just what I needed to see.

Sorry, I'm having to deal with some problems in another forum at the moment.

I recognize you are in a rush to get ready, so the short answer is:

1. Add an additional fused (and fat, if you like) charge wire from the B+ back of the alternator to whatever batteries you want to charge, and leave the OEM wiring alone.

2. Do not rely on the OEM trailer battery charge circuit (that feeds the 7 pin trailer towing / truck camper receptacle) that normally would be adequate to charge emergency trailer brake batteries while under way.

3. Figure out your house battery isolation scheme. Relay recommended. Flyback suppressed for extra points.

4. Run your own fused (and fat, if you like) house battery charge wire (separated by your isolation scheme of choice denoted in Point #3) to a sturdy and safe quick connect /disconnect plug / receptacle assembly for when you remove your truck camper.

I'll be back to this thread later, in a couple of hours or so, with those diagrams.

 

You have a GPCM...the other relay I believe is for the air intake heater...which appears to have been removed and replaced with a boost gauge sensor

 

@Yota4r

 

No worries, no rush. I’m feeling pretty good about the install. Thank you!! I haven’t fired up the truck yet. Started raining so I’ll finish it up tomorrow morning. To follow up on your 4 points.

1. New alternator wire is a 1/0 running from alternator to drivers side battery. Stock wire will also remain hooked up to the alternator to the passenger side battery. I will have to cut the end off it to put a lug with a bigger hole so it can fit onto the new alternator post. Looks like stock cable is 6awg?

2. I’m not relying on the oem trailer harness to supply anything other than power for the camper lights while driving

3. The Victron dc-dc charger has its own isolator in place. It senses engine start/shutdown automatically by voltage. When it senses the truck batteries have dropped below 13.5v, it isolated them. When it senses over 13.5v, it joins them to start charging camper battery bank. I’ve used them in the past with no issues draining starter batteries.

4. Camper battery bank is hooked up with an Anderson connector so I can disconnect when I remove the camper. It also has its own 60 amp fuse where it hooks up to the truck passenger side battery.

Final questions are basically what was asked in point 1. I should be fine leaving the oem alternator cable hooked up on both ends (alternator to passenger battery), along with the new 1/0 cable ALSO hooked up to alternator to drivers side battery. Fused with a 300amp fuse. Stock cable is 6awg?

Awesome! Noted, and I appreciate the knowledge. Your posts have been a huge help leading up to me tackling this. Thank you all!

 

Looks like Y2K posted as you were responding, Hopefully you caught that he came back with his info

 

I did. I now see why that wire is so crucial. It does a lot more than just supplying charge back to the battery. It will stay connected along with the new thicker cable.

I guess the next thing I’ll be trying to figure out will be a way to regulate the glow plug voltage so I don’t fry them with the bigger alternator. Until then, I’m gonna wait 2 min before starting the truck. I’ll get a voltage meter for the outlet in the cab so I can start watching voltage drop (glow plugs on) and voltage rise (glow plugs off). I’ll be doing more research in the forums from old posts on what other people have tried.

 

One more diagram, for your particular 2002, is coming in a bit.