Missing Fuses, and battery draining when cars off

[Jai Bunney]

That is called a ground loop and it means something plugged into the audio system is earthed in two places. This will cause an annoying hum but won't drain the battery unless it's getting power at all times.

Since these cars are getting older now, a common fault is the alternator diodes fail. as the alternator is directly connected to the battery, the diode is a one-way circuit for the battery to be charged by the alternator. When this fails, it will allow the battery to simply drain away.

You can disconnect the 12mm bolted wire going to the alternator, and if the battery seems to last, then replace your alternator (alternator, voltage reg and diodes are one unit)

Mike

The guys at the dealership tested the battery was getting charged by the alternator and according to them it was... Is there a way to test the alternator directly with the multimetre? Or is it something thatd have to be done by an actual mechanic or auto electrician (hopefully not either ��)
Took the car for another drive just then and came back and the battery went more red than green... Will swap over tomorrow with another battery and hopefully it is just a dud battery not holding charge.
But if it happens to another new battery is the most likely cause a bad alternator? Or in theory should that even be draining power when the car is off?

[Jai Bunney]

You probably don't have missing fuses. There are slots there that are unused in some cars.

Yea i was thinking that too, just thought id still ask?
And mainly was concerned because at the mechanics shop we opened up another mitsubishi fuse box that was exactly the same as mine and had a fuse in thebsection marked F and G (not dealership, was confusing the two... ignore that)

[Rob's 380]

It will probably be another alternator you need, it may still charge but will allow the battery to drain away when it's not charging, when the car is switched off.

[Jai Bunney]

It will probably be another alternator you need, it may still charge but will allow the battery to drain away when it's not charging, when the car is switched off.

Fuuuck. Is there any way to check for that myself?...

[cooperplace]

yes, multimeter. A fully charged battery is about 12.7V, charging system puts out 14.4v when charging. Just measure across the battery terminals with engine on and off.

[rumpfy]

J, Can I suggest you take it to a electrical guy who should be able to diagnose the problem in about 10 minutes.
One needs to use an amp meter to measure the current flow out of the battery when everything is switched off.
This current should be about 50 milliamp maximum and is due the standby current used by the computer and remote keyless entry system etc..
If the current is say around 500 to 1000 milliamp it is probably the boot light or glove box light not tuning off. If the current is more than say 2 amps, then it is likely to be the alternator diode/s.
Either way one needs to use an ammeter.
Use of a voltmeter for checking the system voltage is correct, however if the alternator is not charging, the easiest way to check this is to run the car with the engine idling, then turn the headlights on. If the charging system is OK, the motor will slow down slightly. The slowing of the speed is due to the charging system having to supply the extra power to run the lights. This increases the load on the motor, so it slows down.
Hope this helps.

[Mattsubishi]

A manual isolator switch and some alligator clip cables from Jaycar make testing for parasitic drain a lot easier. You can attach the but of the switch to the negative lead clamp and then attach it to the negative post. Unscrew the switch so it's open. Set your multi-meter to 20 amps dc. Use the alligator clip cables to attach the multi-meter in series to each side of the open isolator. Parasitic drain should sit at or below 0.03amps. It it's higher than this try disconnecting the little square pluge on the alternator and see if the reading drops to an acceptale level at or below 0.03amps. Then plug it back in and see if it goes back up again. If so it's a faulty diode in the alternator. Replace the alternator. If it's not that you can disconnect the multi-meter. Close the isolator by screwing it down. Set your multimeter to 20v dc. Check each fuse by touching the probes to the contacts on the back of each blade fuse. Anything other than 0.00 means there's a voltage drop and that's the problem circuit. As a bonus you can use the isolator switch to prevent parasitic drain until you figure it out.

[Jai Bunney]

Thoight I'd clear things up here, turns out the new battery I had bought has a "faulty" eye. And the red/green was very unreliable as the mechanic checked volts and the alternator and everything was fine even when the battery eye indicator said it had low volts and car was starting fine.
Old battery died from my miss use of the stereo when the car wasn't running multiple times.
And the fuses were just spare fuse slots. Thanks guys anyway.

[Gavdore19]

I put a dual USB socket instead of the cig lighter socket into missus focus. When she left a cable inserted it would drain the battery. (guessed it was like pressing down on lighter constantly) pulling the cables out when the car was off solved the issue