Engine barely starts after trying to fix fuel tank switchover

[Sofes]

Hey guys,

Just a bit of a brief rundown, dad bought a 89 td42 NA and the previous owner had installed a axillary fuel tank which a switch to change between which tank was running. Dad thought that it wasn't working or switching over.
So we followed the wires and found 2 relays under the steering wheel connected up to the fuel tank switch.
Now silly me and my curiosity took one of the relays out and started the car. Now it ran fine then obviously it starved of fuel. I put it back in and started it on the other tank and it ran then was starved of fuel again.

So now one tank barely works (only when I'm cranking and accelerator pressed fully down, starts to chug then goes, only to starve again) and the other doesn't work at all.

I have primed and bled the fuel system from the fuel filter. However that is fine.
My next suspicion is that there's air in the injector pump or injector lines.
I don't particularly want to go near those haha

Apologies for the long post but I'm worried I've f***** dads car!

Any ideas of where to start? Or just take it to a mechanic?
Any help would be appreciated!

Cheers!

[PeeBee]

Unsure what vehicle and engine, but cracking an injector and priming thru that to push the air out won't hurt anything. Keep going, it should come good as long as the supply tank has fuel and there are no air leaks