2007 peterbilt 387 Gauges not working

All my gauges quit working. 2007 peterbilt 387. Electronic log won’t flip over to drive mode. If I unplug the speedometer everything goes back to normal except the speedometer and the ELD. Some friends say replace the speedometer head. I don’t know

 

If all your gauges have bit the dust its more than likely a fuse has blown.

 

We don't need no stickin' gauges!

 

Not sure on that model but a 379 has a relay behind the left dash panel, acothere are two, sit back to back. The smaller one closes the big one and it powers the gauges and other things, when going bad it doesn’t close completely and crazy things happen.

 

You have a problem with the communications bus which runs the eld, speedometer and most of the gauges, if you unplug the speedometer and everything works than more likely than not it is a defective speedometer. You can get it repaired or buy another one - used are out there.