Megabus wiring diagram

Tiny
ARDIUS79
  • MEMBER
  • 2017 FORD F-150
  • 2.7L
  • V6
  • TURBO
  • 2WD
  • AUTOMATIC
  • 67,000 MILES
Greetings!

I am searching for an image, a diagram, or even just an explanation as to what goes to the Megabus attached to the fusebox. I understand the positive battery terminal consists of the starter red wire, and then the other large red wire comes from the Megabus to the alternator, the green wire goes to the BCM, but now I have an open spot on the Megabus, and only a ground wire without a place to go. The Megabus appears to have a grounding spot, but upon further inspection, that spot attaches to the other Megabus locations, which doesn't make sense to attach a ground in this same location.

If I had an image of the correct wiring of the Megabus, and the battery terminals with a brief description of what goes where, I'd be in good shape. I've attempted to guess previously, but unfortunately, there is no power at all. Any suggestions as to what I may need to check would be very helpful. I've checked the appropriate fuses and will be replacing most of them, as well the relays tomorrow, just in case.

Thank you in advance for any assistance you can provide. I greatly appreciate it!

Best regards!
Friday, August 29th, 2025 AT 6:53 PM

8 Replies

Tiny
STEVE W.
  • MECHANIC
  • 15,233 POSTS
There is no ground wire near the fuses. The Mega fuse is the main power fuses for the entire truck. Connect a ground to it and if you are lucky it will only burn up the wire.
The Green goes to the electric power steering not the PCM. What color is the "ground" wire.
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Friday, August 29th, 2025 AT 9:46 PM
Tiny
ARDIUS79
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  • 18 POSTS
Okay, so what connects to the mega bus? It's not the starter. The starter connects straight to the battery. So that leaves the 300a, which the alternator, the the green, which leads to the power steering, and then what goes to the last spot? I have no other components that I can find that need to be connected and no other wires needing to be connected, with the exception of the ground wire, which I believe goes to the transmission ground location and attaches to the negative battery terminal.
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Sunday, August 31st, 2025 AT 12:29 PM
Tiny
ARDIUS79
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  • 18 POSTS
My apologies. I just saw the diagram you sent. That is precisely what I've been looking for. Thank you, very much!
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Sunday, August 31st, 2025 AT 12:37 PM
Tiny
STEVE W.
  • MECHANIC
  • 15,233 POSTS
No problem. If both the power steering and alternator are on the 300, they shouldn't be. The steering goes on the 125 with the alternator on the 300. The 300 is actually there to protect the battery and vehicle systems in the event something in the alt fails. Plus the alt is rated at 215 amps so not a lot of overhead if there is a problem.
No problem not seeing the image. As I said though, there are no grounds to the BUS fuses. Normally there will be 2 larger grounds, One goes to the engine another to the frame, then a third that connects the body and frame. Perhaps your ground is one of those or maybe not used.
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Sunday, August 31st, 2025 AT 11:36 PM
Tiny
ARDIUS79
  • MEMBER
  • 18 POSTS
I've gotten the wiring issue solved and everything is back to where I started. Unfortunately, the initial problem was a crank, no start issue. It turns over, but doesn't fire. It sounds terrible too. Like a grinding of bad brakes. Further, when I release the key, the truck continues to try and start. Typically, it should cease when I let off the key and it doesn't. It only lasts for maybe 1 or 2 seconds and then it dies out. Not sure what to make of it. I've changed all of the fuses, most of the main relays, et cetera. Even fuse 37. I'm beginning to think it may be the fuel pump, but the grinding noise doesn't help that argument. I've got a new ignition switch that I can put in but I don't think that's it. Any suggestions?

Thank you, sir!
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Tuesday, September 2nd, 2025 AT 6:20 AM
Tiny
STEVE W.
  • MECHANIC
  • 15,233 POSTS
The starter that stays on is typical of newer vehicles. Many are set up so the starter relay stays on until the engine starts with a time out timer of a few seconds. Can you make a video of the problem and then ask a new question saying it's a crank no start. (We try to keep queries to one topic to make searches easier) Include the info of what you have tried.
The grinding might be a damaged timing phaser but it's hard to say without hearing it.
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Tuesday, September 2nd, 2025 AT 10:08 AM
Tiny
ARDIUS79
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Okay, will do. And you're probably right about it being a timing phaser. I recently had problems with the cap that holds the solenoids. I'll ask a new question now with video. Thanks.
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Tuesday, September 2nd, 2025 AT 5:03 PM
Tiny
STEVE W.
  • MECHANIC
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Thank you.
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Tuesday, September 2nd, 2025 AT 6:33 PM

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