B737-800 flight crew reported Ground Conflict with vehicle parked on taxiway.

Narrative

We landed Runway 10R and cleared at XX Taxiway. My FO (First Officer) contacted Ground Control and told them we were assigned Gate XX. We were instructed to taxi on Taxiway XY and hold short of XZ for traffic in the alley. It was a dark night under low overcast skies with wet surfaces and we were in an older 800 with the incandescent lights which makes it harder to see; especially with the bright LED lighting on the taxiways and terminal. As we turned west-bound on Taxiway XY the FO was heads down talking to company and finishing their after-landing flow and checklist. I was also partially heads down checking my after-landing flow and checklist and verifying the state of the jet when I just barley caught sight of an object on the taxiway in front of us.I turned on all our landing lights and could then clearly see an unlit and unmarked truck parked on Taxiway XY just south of centerline at the XA Taxiway between Taxiway XB and XY. When I had our parking brake set; it was much darker and harder to see the truck with normal eyesight in the real-life conditions that were present at the time of the incident.I brought the aircraft to a stop and called Ground Control. They did not know anything about the truck and called an Operations Vehicle to investigate and asked us if we would like taxi around the truck onto Taxiway XB via Taxiway XA. I said no as I did not know what else is going on out there and could not see well. Several minutes later there were Operations Vehicles on scene and told Ground that we would be clear to taxi around the parked truck on Taxiway XA onto XB; which we did very slowly with all our exterior lights due to the situation in the low light conditions. I felt comfortable continuing in the way we did since there were ZZZ Operations Vehicles on sight who told Ground we were clear of the unlit and unmarked truck.I called ZZZ Tower on the phone after we blocked in. They said they had no idea what happened and never knew that truck was on the active taxiway they cleared us through. They said ZZZ Operations had shut down that area of the airport at this point and they had no idea what was going on.The unlit and unauthorized truck could have been easy to miss on the active taxiway as there no reflective materials on the truck and the paint was a dark yellow. If we hit it; it would have been with our number 1 engine; which was running at the time. It would have been even more catastrophic if that truck was on the active runway.I have been watching Company replace their incandescent exterior lights on their [type] aircraft with LED lights. It makes a significant difference in visibility compared to our old incandescent lights; especially with all the new LED lighting on the airfields which can be blinding in the flight deck. It would have been much easier to have seen that unlit truck parked on the taxiway if we were in a newer aircraft with the LED exterior lights; or if we were in one of [the] retrofitted NG aircraft with LED lights. Can we please look into how Company got the LED retrofits of exterior incandescent lights on NG aircraft.