1999 Peterbilt 379 2ws cat Tac and Speedo not working

Tach runs off speed sensor on flywheel sensor , plugged into bell housing - speedometer off sensor on tail shaft of transmission - watch out, there maybe one, or two - one at 12 o’clock, one at 7 o’clock - one runs to speedometer head, one to ECM.

Does cruise control work currently?

 

Could be that both gauges aren't working. I had to replace the speedometer on my truck about 6 years ago, which would make yours around the same age as mine was then.

 

It’s a fuse

gonna be on the right side of fuse box marked ign acc or something like that. You probably have a couple other gauges not working as well

 

Are both these sensors on the engine? Or the transmission?

If you’re looking at the engine bay you’re in the wrong place.

 

Hey guys I’m having a similar issue to this as well. I just bought a 97 Peterbilt 379 and all the gauges work but the RPM/Tach gauge. I know there’s power to it but when the truck is on and running it just stays at 0. But when I shut it off it jumps up between 2k and 2500. I sent out the tach to get rebuilt but they tested it and said everything is working how it should on it. So wondering if replacing that same speed sensor on the flywheel would help.