M1009 GPR Electrical Wierdness

[tgtaylor64]

Can someone help me troubleshoot this? Stock M1009, 24 VDC setup, going through resistor bank. Multimeter ground to rear of driver side alternator, positive to top of glow plug relay - reading 24.5 VDC, everything off. Upon startup, engine cold, I read 7.5 VDC at this point while the glow plugs are heating. Why only 7.5 VDC? If I connect the positive lead to the bottom lug (to the GPs), I get about the same. I just replaced my relay thinking it was pitted or fouled. The new one is reading the same! By the way, I get the same response whether I feed the top lug from the resistor bank or the 12 VDC diamond (of course, I have only 12.6 VDC or so on the top lug before I cycle the GPs, then it too drops. What is happening? Where am I loosing 5 or so volts? All connections are clean, shiny, and greased.

 

[antennaclimber]

Sounds like you have a battery failing under load or a connection failing under load.What is the battery voltage of each battery when you turn the GP's on?

 

[tgtaylor64]

Thanks, Antennaclimber, this is the ideas I need. I checked the voltages of each battery while the GPs cycled. Front went from 12.7 VDC to 11.9; the rear went from 12.6 VDC to 11.9. I am getting the exact same reading from the top of the relay when closed as the bottom (as expected); but I am getting 7.5 VDC to the GPs! Oddly enough, the truck starts like a champ; however, I doubt that will be the case come winter in SC!

 

[tgtaylor64]

Not many connections. Twelve volt feed from diamond is direct to negative post of rear battery. Twenty four volt feed is via bus bar.

 

[antennaclimber]

Keep checking each part of the system. Work your way back to the batteries. Make sure you have a good ground connection on your voltmeter. Try using the front battery Negative terminal and measure your voltages again.

Eventually you will locate where it drops out.

 

[tgtaylor64]

When I use the front battery negative post for ground I am getting 12.5 VDC at the GPs! I have always used the drivers side alternator negative post as ground because it is so convienent! Whew. Now I feel better...right? Or is something else amiss?

 

[PJL]

Mine does the same thing. With no load on the resistor bank you will see a higher voltage after the bank. When the glow plugs are cold they draw a lot of current. It will drop the voltage at the relay down to single digits. As the glow plugs warm up they draw less current and the voltage will rise. Try leaving the multimeter connected during the entire cycle and see what it does.

 

[antennaclimber]

When I use the front battery negative post for ground I am getting 12.5 VDC at the GPs! I have always used the drivers side alternator negative post as ground because it is so convienent! Whew. Now I feel better...right? Or is something else amiss?

Start checking and cleaning all of the ground connections on the alternator and the battery ground wire. See if the voltage comes up after cleaning.