# 1990 nissan 240sx with ka24de battery draining when lights are on



## Shitmissile1990 (Oct 6, 2019)

Not sure if I found the right place. And it's my first post so I'll do my best to explain everything going on. I have a 1990 240sx. Swapped to a ka24de. Recently got it running somewhat. But there's a serious issue with the charging system. It will idle fine and drive normal with no loads on the charging system. But as soon as the headlights turn on the idle gets rough and drops from 500-700 rpm. Same when the brake lights turn on. Battery was brand new. And the alternator was replaced about 2 years ago brand new. It also drains the battery if I leave the negative cable connected with the car off and key out. I'm just curious as to if anybody has had these problems. I fear it's time for another alternator but I figured I'd ask here before I start dumping money into it. Checked grounds. Grounds are in ok spots. Is there something common that causes this to happen? The drain when it's off is not super concerning but the drain while driving with lights on is. Not blowing fuses. Not having any issues with no electronic loads. But as soon as there is it acts up. Any advice or help on what to look for would be very appreciated as I'm not too good with electronics.


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## rogoman (Dec 16, 2004)

A properly working charging system puts out about 14.1 to 14.7 volts for your car. A battery should have a static charge of 12.2-12.6 volts. If a battery is not good, the charging system may not be able to charge properly. If a vehicle is not charging properly and the battery is good, the first thing to do is to turn the ignition switch to the "ON" position without starting the engine and make sure the charging system warning light is operating. If the bulb is burnt out, the charging system will not charge. If the bulb is OK but still does not illuminate, the circuit must be tested. If the warning lamp does illuminate, then the next thing to check is to make sure the circuit between the battery positive post, or fusible link, to the connection in back of the alternator is good. On Nissans, this will be a thick (approx. 10 gauge) white wire to the "BAT" post on the back of the alternator. It's not uncommon for this wire to get corroded and burn up, creating resistance in the circuit. So, before assuming an alternator is bad, make sure this circuit is good and battery voltage is getting to the alternator. It's also important to make sure the alternator belt is tight and not slipping and the battery connections are clean and tight.

Assuming the charging system voltage is ok and the battery is good, the next thing to do would be to have a parasitic draw test performed; there should not be more than a 50 milliamp draw on the system with the ignition switch in the "OFF" position. If there is a higher draw, you need to do some testing to find out where the draw is coming from. Remove fuses one at a time until the draw goes away or falls into acceptable range.

Also, it is NOT a good idea to disconnect a battery cable on a computer controlled vehicle while running to test the alternator. This is a good way to damage an ECU. When a charging system is not charging, or overcharging, a lot of "strange" things can occur. It's not uncommon to see a multiple of stored trouble codes in the ECU memory. So, whenever a car is setting a multiple of trouble codes, idling funny or stalling, or anything out of the "norm," test the charging system before you start pulling hairs!

When replacing electrical components such as alternators, starters and distributors, fuel injectors and sensors, always replace with new or reman'd Nissan OEM components; aftermarket components generally don't last long, don't work right and many times are DOA.


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