Fuel shut off solenoid

I have a 1991 peterbilt 378 with a Detroit 12.7 60 series, where is the fuel shut off solenoid?

 

That’s what I have about decided

 

It started running weak, not bad but would have to drop a couple extra gears when loaded on hills that I wouldn’t normally have to. Took it to a local guy to have it scanned because my normal guy that comes out has the flu. When he tried to scan it there was no power to the diagnostic port. Brought it back, traced wires, found a relay in the dash. Pulled the relay to check connections and put it back in and then I had power to the port. Next day went back to the local guy and he wound up not being there. It did not run good there and back. Checked power to the port when I got it back home and still had it. My normal guy come out 4 days after that tried to scan it and no power. Tried the relay again and put a new one in, still no power. Tried to crank it now it won’t crank. Checked fuel pressure to the secondary fuel filter and it is 75 psi while running on either. Trying to take off line from secondary fuel filter to the back of the engine to check for any blockage or bad places in the line. It’s in a very bad place so haven’t gotten it off yet but working on it. I’m thinking it’s the ecm but trying to rule out everything else before I drop $2,000

 

I got the truck fixed. When I was checking for power I was missing the hot wire from the ignition. A man told me which wire to check and sure enough it was dead. Jumped a wire from the battery and it cranked right up. Thanks everyone for the help