low voltage while pressing gas

Sounds like there might be a wire that is being shorted out

 

gas?

 

Seems he changed it to accelerator.

Remember though that some, like me, drive trucks fueled by natural gas. So yes, gas could be an appropriate term in today's environment.

 

Most trucks the cluster information is feed data straight from the engine. So if your cluster is reading low voltage, this also what the engine ECM is seeing. Most engine ECMs get their own power feed, usually from the batteries via a separate harness. When you see voltage drop like that, it is because the power feed is bad somewhere and the ECM is starving for power. Most engines use a bit more voltage to fire the injectors longer under higher engine loads. This is why the voltage drops when under load, or throttle pedal pressed.

 

Some trucks have a wire direct from the alt to gauge. If belts are slipping with RPM increase could do that. Belts loose or hard? Worn alt pulley?