1985 Cali-spec 300TD. Parked it last October/November when it was due for Virginia safety inspection, and it would not shut off except by using the Stop level (didn't think the inspectors would be too keen on this...)

Replaced the IP shutoff valve (thanks Diesel Giant for the pictorial), and it turns out the issue was due to a vacuum leak in the door lock system. C'est la vie.

Bigger issue is that since I started the car up, the tach is now non-operational, meaning the A/C is too. Scheduled to take the family to Ohio Memorial Day weekend, and I need the A/C.

Tach sensor measures 1.85 K Ohms, and at idle is putting out 5.62 VAC. I would like to check input to the EGR computer, but what is the trick to getting the wiring harness connector off? Where else can I check at after the EGR computer to verify the latter is not bad? 10 amp fuse atop the OVP is good. Can you check voltage to the OVP, and if so, on what sockets/pins?

Fuses in the fuse box are also good.

Assistance please.

Thanks,
Dave