Hooked up battery backwards car will trun over but seems like there is no spark

You didn't say what sort of charger and what it is you are trying to charge - this is the cars and trucks section but it would be too easy to assume you are asking about a charger for car batteries.

The multimeter should clearly indicate the polarity of the wires or plug and verify your assumption it is incorrectly connected internally.
It isn't unusual that a discharged battery causes a spark when being connected to a charger the right way around and it isn't unusual that a completely discharged battery will demand more current than a charger can provide causing a modern intelligent charger to shut down, similarly a defective battery can spark when connected...

If the charger is really wrongly connected internally it shouldn't be very difficult to rectify with most designs and if you provide more information in the comments I can try and advise you further.

Just as a matter of diverse interest, with lead acid batteries maintaining correct polarity is very important as when completely discharged it is possible to recharge them with the wrong polarity and when attempting to reconnect such a battery, it will immediately destroy many of the electronic circuits it supplies...

It should be willing to start even without the O2 sensor. Check that you're getting spark, check fuel pressure.... Check if any codes.

Try charging the battery more. Even though your lights may come one, starting a vehicle requires massive amounts of amperage from the batter. It's possible that your jumper cables aren't a thick enough guage to supply enough power as well. Sometimes the vehicle you're jumping from might not have enough power to support your vehicle's starting power requirements.

No. Replace the Engine control unit that was destroyed when you reversed the polarity to it.

You will need the whole system inspected for dmage.

can be grave, some electronics blow up , backwards.
so, find an object that is dead. my guess, is the EFI is dead. huh?
so do you have 12vdc to all ECU power pins, or not , keyon.
if not you blew a fuse or fuse link. trace the path of lost power....
many ECU's have a diode inside protecting them from reversals.
not all do. 89 is like the dark ages in ECU. (first gen)

you try to crank the car with the battery hooked up backwards?

How about after you fixed it?

You probably cooked a major fuse or relay. I would look them over again. Some are shielded and not easily seen.
Hopefully a fuse took the blow instead of the ignition module or computer.

its your ignition module, this will fix your problem.. any time you cross spark the battary its the ingition module... good luck keith....

have you checked all ofyour fuses? usually when you hook up a battery backwads you end up blowing a fuse and or fry your alternator on older modeled vehicles as there is no protection for it.