Originally Posted by Ragtop69GS
After much searching here and googleing with no luck, I come to the best place on the net for advice.
I have a 2002 Dsdp with an ISC 350 on a spartan chassis. I located my diagnostics port under the dash and also found these 3 switches, I can find no mention of the switches in the Cummins or Spartan manuals I have. Could someone please explain these switch functions or point me to a web link that will explain them.
The switches flash a light on the dashboard to advise what failure code has been set in the system that is switched "On" using those switches.
The round connector is for a scan tool to be connected to get same info plus more. Your year vehicle would have J1708 protocol (heavy truck prior to J1939). It is NOT OBDII, but serves a similar function.
The connector is likely a Deutsch 9 pin. There should be another one around the trailer hitch area to bring the scan tool to the engine area.