Low voltage on interment cluster when running.

[PeteinSF]

Hi All,

This is a summary post of an elusive problem I had from day-one and also looks to have left the factory with the issue. The symptom was that the instrument cluster voltage reading would drop into the 9-10 volt range when the engine was under heavy load. For those of us with DT466 you can hear the injectors fire and their duty cycle, you can actually hear the load. The perplexing part was that everywhere I measured the voltage it was the normal 13.8 to 14+ volts that I expected. Also when the indicated voltage was very low (normally climbing i hill) i would get “water in fuel” and another lamp warning (I can’t recall what).

With that I started hunting for bad grounds all over the bus. Replacing terminal lugs on grounds, scraping paint. Before my long trip from Calififornia to Niagara County I spent days tracing wires with no success. The trip went fine but always at a low indicated voltage.

In NY I started to clean up the battery box and fixed all the battery cable lugs, replacing fuse holders etc. After cleaning all that up one day the bus would not start. Cranked ok, it would run on starting fluid but no sustained operation.

My hunt then went to finding the bus’s chassis electrical diagram. Located online I found that all of engine’s critical functions are powered via the two “clean power” 8 gauge harness via two 40amp fuses connected directly to the battery.
Knowing that I then traced and fixed the lack of running by jumping around the relay that powers the injector module. In monitoring the voltage at the relay jumper I found 10-11 volts (when running), not the 14 at the battery. (Finally).

Hmm, the diagram showed the relay was directly connected to the battery. Where did the 4 to 5 volts go? I also noticed the current was rising dramatically as the voltage dropped.

So, there is a factory looking “Y” splice in the “clean power” battery feed close to the starter. The plastic insulation around the splice was discolored and cracking. I then started the bus crawled underneath and grabbed the splice and found it very very hot. Cutting it open I found that only two strands of the 8ga wire were actually connected. Not due to heat or melting, but via a horrible wire stripping job. I suspect this bus has always had this problem. As note, the low voltage/high current passing through the relay melted the internal contacts and opened the circuit. I am not sure I would have found the source of the problem if that relay had continued to live.

So all you Navistar owners perform a “clean power” checkup, your ECM will thank you for it.