Pull the connector housing off the firewall and check the terminals from the rear side. Some of mine on one of my 1995s were in bad shape. No idea how they got that way. If the rear end of the terminals look OK, check continuity to ground for the E1 terminal (it's supposed to be the ground terminal). Your problem could be the terminal connection inside the connector housing is FUBAR. If it is, you'll need to crimp a new terminal onto it.
It's just a connector housing, like all the others in the truck. Repair is the same for it as for all the others.
The better idea, and I know the FSM says to use a paper clip, is to use a jumper wire, like
the one Joey sells, with terminals crimped onto it. Those are positive connections.
If there is no problem with the connector housing connections, you need to look at the ECM connections, or perhaps the wiring between the DLC1 and the ECM (behind the glovebox).
All of this is in the 1995 EWD (Engine Control) and FSM (Engine Mechanical, Troubleshooting) sections of the 1995 FSM, in the Resources section.
As stated above, you can use the DLC3 (D3 in the picture above) near the fuse box, to reset or interrogate codes, but if you have a DLC1 wiring problem, you need to get it fixed. It's directly connected to the ECM and you could have cascade problems if you don't get after it.