Hi new to this forum. Need some help. Hook up my battery in reverse. Now stater won't crank. Even head light had no power. Only had power to window and heard fuel pump noise. relays, fuse, and fuse link are check good. ECU green light flash only when ignition key turn. It doesn't stay on. Does it need to stay on? Could I fry my ECU? What else should I check for with battery hook up reverse by mistake?

most likely you've fried at LEAST half of your electrical system...including the ECU. Anything that is connected to the battery, and takes power constantly, or when the engine cranks, is likely to be shot...explaining why the windows worked. Electical pumps are polarity based, so although you heard it pumping, it's was likely pumping "in reverse"...

As for the fuses and all, with the abttery hooked up reversed like that, the surge hits the equipment prior to blowing the fuses...

OK, it make sense. Current flow from negative to positive. Fuse won't protect my components. Well fuel pump, power window, door lock work ok. No power to light, radio, and starter motor. So you think my ecu is fry right? Would the ecu control power to the above components. Should the ECU green light stay on if it is good. My ECU flash only when ignition key is turn.

Well, I'd say the ECU is dead.

Simple explanation :

DC electricity flows in only one direction. Any device in the car that is primarily an electric motor (Window regulators/motor assm., door lock accuators, etc...) will simply areact as any electric motor will do when the polarity of the applied power is reversed...they too will reverse. Now, depending upon how the switch itself is wired, this could be quite funny to watch doors unlock, when the lock button is pressed. It is possible to wire the switches so the polarity doesn't matter, as long as power is received by the motor, and flows through the circuit. Your fuel pump should operate on the same bsic priciple, although it is also possible that the fuel pump could have a protective diode circuit built into it, to protect from circuit overload, and short circuit conditions, preventing the power from being sent through the pump in the wrong direction. It also could have simply run the pump motor in reverse. Depending upon pump desing, this could simply continue to pump as normal, or may reverse the flow of the pump.

The ECU, on the otherhand, is not a motor, and it's functions relay on power flowing through it's circuits along a certain path. Unless Nissan took into account the fact that someone might swap polarity of the batter, they did not install a protective diode circuit on the "output" or "ground" lead of the ECU. Therefore, most power would be routed through the computer, utilizing all of the circuits, including circuit which were never meant to carry current at the same time another circuit was also carrying. This type of scenario usually results in a short circuit within the ECU itself...

So, you've most likely fried the ECU as well as any or all engine sensors. If you're unlucky enough to have the digital dash option, you've most likely fried that as well...the combination switch that controls your cruise, turn signals, lights, etc...is also likely fried.

The starter itself may not be fried...but if not, the solenoid definately is. You may also need to replace your alternator, as the built in regulator is likely dead.

These are just based upon my limited understanding of automotive electronics. I hope it helps.

Thanks, today I got a ecu from pickaparts yard and install, and still not working. I already put the battery in the proper polarity. How is that poosible the the fuel pump can run in reverse. Fuel are not on until you turn ignition on. The battery cable was install reverse for less than 5 second and realise it was wrong so I pull it off quickly. The other suspect problem is may be the starter solenoid, but why my head also not working. I don't think my car is digital dash board. My speedometer are dials indicators. You said signal switch might be bad. But what is that got to do with no power to my starter and head lamps? What about starter inhibiting switch. The one that prevent the car from starting unless is in park position. Do you where that is locate. There got to be some short to wiring or a switch or a component. I have try to replace almost everything I can think of and so far nothing work. This car is so good to me I can't let just die like that.

You also fried the security system whenever you reversed the polarity, since it's also a computer based system like the ECU. It also kills the starter whenever it goes off, so it's possible that it's preventing you from starting the car. Does the security light flash whenever you open the doors? Also, does it go on when you lock the doors and stay on for about 30 seconds? Keep your window opened after you lock the doors, then after the security system is activated, pull up the lock and open the door from the inside. Your lights should start flashing and the horn should start blaring. If you think the security system is dead, try disconnecting it, then maybe your car will start, but I'm sure you also fried the starter solenoid and the voltage regulator inside the alternator anyway.

The reason why the fuel pump may go in reverse and start sucking fuel back into the tank is because of the reversed polarity, as maxwgn stated. Didn't you ever take one of those cheap toy cars when you were a kid and put the batteries in backwards and the car went backwards? Well, it's the same principle. But like maxwgn said, some things don't work that way, especially computer circuits.

-C-

My car is a 1984, and I don't think it has security computer. I don't remember read about it on the repaire manual. I disagree with the fuel pump runing in reverse, because now the battery cable is already back to the normal position. And the fuel pump only come on when ignition key is turn. I never had the battery hook in less than 5 second. And ignition key was not on. I do agree that my starter solenoid might be fry, so I am going to get another one. Does any one have any idea how to test the starter soleniod with the starter on the vehicle? I don't see how my voltage regulator would prevent the power to my starter and ignition switch. Any way the voltage regulator on my car is a electro-mechanical type and is not on the alternator. Is mount behind the relay box. By looking at the wiring diagram, the starter soleniod is connect in series with the inhibiter switch. The inhibiter switch is what stop the car from starting if the transmision shift is not in park position. Now what I want to know is where is that switch locate? That might be my problem.

An '84 shouldn't have a security system. It's been awhile, and I'm trying to remember how it went when a friend of mine positive grounded his MG B (honest mistake as the DAPO had a black cable for + and a red for -). The alternator burned, the fuel pump pulled the gas out of the float bowls, the fuel cutoff switch burned and I believe the starter was toast. You may have other problems as your car has much more electronically controled systems than the MG would have had. If you have a VOM or a multi meter get in there and start checking for current and how much.
Good luck and keep us posted.
BTW: to check the starter you should be able to ground across the two terminals on the selenoid, or with it out (not hard on the L motor)hook up a battery charger (not more than 10 amps) or jumper cables from the battery, pos. to the posts on the selenoid, neg. to the case. With it out you will be able to see wether or not the bendix is engaging properly. Use caution and use common sense. Safety first and all that.
Johnny Lang

Just test the starter soleniod by connecting batt. + to smaller terminal on the soleniod and the starter does engage, so the starter soleniod is good. The next item to check will be the neutral switch (inhibiter switch) or the ignition switch. Is the neutral switch locate on the transmision shift handle? And I will check also the security computer also. Will update on the finding.

Did you try pushing the lever in park up more. Sometimes when I have my car in park it doesnt turn on because of the switch not being touched so I have to push it up to touch the switch then she starts.

Starter soleniod test good. Put shift in park and neutral with no start. Next thing I want to do is check for the neutral start switch. And see what happen from there. Will let you know what I found.

Test the inhibiter switch according Haynes repaire manual and it test good. Took out the ignition switch and open the switch and contacts inside the switch looks fine. The next thing is checking for broken wire. May have to trace all the wires for continuity from the starter soleniod to the ignition switch.

Test every components that are suspect, but no luck at all. Might have to get a meter and check for voltage to every components. Might have to end up paying some mobil mechanic to come over and do more trouble shoot after I gave up.