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1993 6.2 with electric lift pump....Unfortunately we do not have a 1993 set of truck manuals on the Forum. So here is a SWAG:
On a 1995 6.5L TD with an electric lift pump, the lift pump is powered through the Oil Pressure Switch (OPS). The OPS is mounted behind the driver's side head. See the pictures here: https://www.dieselplace.com/forum/63-...tml#post702583
. The OPS serves two purposed: (1) powering the oil pressure gauge (2) sending electrical power to the lift pump when it sense oil pressure and shuts down the lift pump when there is no oil pressure.
The OPS can burn out in the part that powers the lift pump but work fine to power the gauge.
If you can locate the OPS where I think it might be, see if the wiring harness has three wires coming out of it. IIRC on my 1994 they are orange, gray and brown. If you have 3 wires, I am guessing your lift pump is powered via the OPS.
Another thing to look for is the Lift Pump Relay. Here is a picture: https://www.dieselplace.com/forum/63-...ml#post6784033
. On the 6.5L trucks this relay is mounted to the passenger side of the firewall. The second picture shows how to jump this relay to power the lift pump. If you have this relay, try jumping it to see if the electric pump works by opening the WIF drain.
If it works, the lift pump is fine and the OPS needs to be replaced. Again I am really guessing here, but if you have a bad OPS, get an AC Delco D1808A OPS. Do not waste $$ on any other brand as the other brands burn out about as fast as you can install them.