2015 Ford F550 6.7L - Electrical Issue
 

2015 F550 6.7L - this morning started it and got going down the road. Hit a bump and the cluster lost power, the power windows lost power, and the AC was on but I couldn’t turn it off or adjust it at all. Went back to my shop and turned it off and back on. Started fine, everything worked for about 5 seconds, then I get a Check a brake system alert on dash, then cluster dies, AC works but can’t be adjusted, abs power windows stopped working. Turned off and on a few times, same result every time.

Battery voltage is good at 12.9 both batteries, alternator is putting out 17V, and I pulled the fuses I thought could be related, such as vehicle power, ECM/pcm, etc. All were good.

Where should I go to next? ECM, a short somewhere? Where is the ECM located? Wonder if I’ve got a corroded or loose plug. It is a work truck for snow removal and landscaping, so corrosion is common. I was also going to look at replacing the ECM relay.

Otherwise, I’m guessing a short or ground issue somewhere, where to start?

My first suggestion would be to find out why the alternator is operating at such a high voltage. 17 is way too high.

If there is a corrosion problem at the plug on the alternator it could be by passing the regulator and full fielding the alternator without any control.
The PCM does control the alt, but some checks need to be done first before condemning the PCM.