Glow Plug Voltage

[Nelson34]

What is the voltage suppose to be at the terminal plugging into the glow plug? Shouldn't it be 12? I started testing mine to make sure I am getting the charge, but I keep coming up with a range from 7-10 volts. The C/K Truck Service Manual only says a "specified value of B+". Have to have the scanner to interpret what B+ is. Thanks!

[More Power]

What is the voltage suppose to be at the terminal plugging into the glow plug? Shouldn't it be 12? I started testing mine to make sure I am getting the charge, but I keep coming up with a range from 7-10 volts. The C/K Truck Service Manual only says a "specified value of B+". Have to have the scanner to interpret what B+ is. Thanks! With the glow plug connected and powered, it could draw as much as 16 amps. The length of wiring between the batteries and an individual glow plug contains some resistance, which will drop the voltage to something below battery voltage. It's an Ohm's law thing. Without the glow plugs connected, you should read exactly battery voltage at each glow plug terminal.

"B+" means battery voltage, in this case.

MP

[Nelson34]

Def. checking with terminal unplugged. Possibly relay problem since getting different readings?

[BUZZ]

I think if you check the voltage with the glow plug connacted to all 8, the voltage reading is going to be around 10 volts or so due to the electrical load.
Buzz

[moondoggie]

Good Day!

Connect the positive meter lead to a positive battery terminal, & the black meter lead to a glow plug connector.
</font> If you disconnect ALL EIGHT glow plugs, you should see 0 volts when you cycle the glow plugs. This indicates that the glow plug connector is exactly at battery voltage - no voltage drop between the battery positive terminal & the glow plug terminal you're testing. This is good news, but of limited value - it's more important to know what happens when a normal load (the glow plugs) is connected.</font> If you connect all the glow plugs, you will be measuring the voltage drop between the battery positive terminal & the glow plug terminal. This is much more valuable information for determining if there is an excessive voltage drop, which could be caused by many things (bad wires, bad terminals on the glow plug relay, bad glow plug relay, bad crimp(s) in the wiring harness, etc.).</font>The actual voltage at the glow plug terminal is valuable info too, it's just different info. It's less useful for troubleshooting bad connections, because it varies depending on battery voltage. For the test I've described, battery voltage doesn't matter, unless the batteries are dead.

Blessings!

Brian Johnson, #5044