Starter didn't crank after installed new injector and o2 sensor

[3r1c]

So my 240 was running on three cylinder cause one of the injectors was bad so we installed a new injector with a new 02 sensor. Then the car battery dropped 7 volts. Next day we put in a new battery and now the starter won't crank. Before we installed the new injector and o2 senor the starter crank the engine over fine. It also have new spark plug and wires. This is really weird. Help me guys

[x240xdrifter]

check all connections in the battery circuit, make sure your alternator is all connected and properly working

[Nismofreek823]

its a long shot but if the injector didn't seal right when installed, your #3 cylinder could have filled up with gas when the key hit the on position. if the valves were closed it wont crank over at all(hydrolock). try pulling the plugs and see if it cranks.

[3r1c]

^^^ Hmm that might be it cause when we try to start the car the starter made a faint noise and then started clicking. So I'm thinking it might be a hydrolock cause the starter can't be shot on the next day. We are going to pull the spark plugs and see what happens.

[3r1c]

Okay we try to jump the starter and it works. Now I may be thinking it can be the starter relay and it seems a common problem from other threads about there starter crapping out on them.