Hooked the battery up backwards

Check fuses first thing a few probably blown from hooking up backwards also have your alternator checked if battery keeps going down if you have a voltage meter reading battery with engine running should be around 14 volts if alternator is charging if not check alternator main fuse

No it won't start if you take the security system out . Because you can't take the software out that's programmed into the PCM/ BCM ! If the PCM - engine computer does not see a key code (pass word ) It will not start the car. Besides that , hooking up the battery backwards probably did more damage then that . Fried computers etc... I have see this more then once , the vehicle's never did work right again . Damaged instrument clusters , charging systems , ignition modules etc...

This doesn't sound like a car, but more like a riding mower or something.

Anyway, is it the magneto that "blew" or a fuse for the magneto? You don't mention that you replaced the magneto....

Some manufacturers incorporate reverse protection diodes that are supposed to cause a fuse to blow if the battery is hooked up backward. Unfortunately, the diode often becomes a short circuit when this happens and would explain why a primary fuse would blow again, even when the battery is hooked up correctly. If you have a wiring diagram for what you're working on, I'd suggest checking for a diode connected near the battery cables. If you don't have a wiring diagram for this, you're probably going to need one.

What can be damaged by hooking jumper cables up the wrong way ...

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Do not connect your jumper cables backwards or bad bad ...

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RedditOct 25, 2012 - Do not connect your jumper cables backwards or bad bad things ...What I'm trying to say is, does this usually happen when you hook the cables upwrong? ... So basically there is only one way to find out for sure what going to .

BY hooking up the battery the wrong way it is possible that you have blown up the CPU and ECM. IF you can get hold of another unit hook it up and see if it starts / fires . IF so the that will be the problem

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.

I would make absolutely sure that I did not hook the battery up backwards, not uncommon.
And in addition to the high current thick cable from the positive terminal to the starter there
is the small connector to the relay on top. Easy to forget that also.

If you hooked the battery up backwards you now need another car as the wiring harness is cooked.

need to have it tested to see if there is a diode in that system they pluginto the fuse panel under thee hood like a fuse but it says diode on top? also have wiring tested at alt make sure you have 12.6 volts at big wire on alt? hope this helps

check all the fuses inside and outside of car.when you hook up battery backwards it will blow more then one fuse.