Electrical problem diagnosis

Discussions about MX5 Alarms, Car Stereos, Lighting, Batteries or other Electrical related issues

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MrGrey
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Electrical problem diagnosis

Post by MrGrey » Mon Jun 24, 2013 7:20 pm

ok, so my car alarm was triggered and I went out to see what was going on and when I tried to use the remote to reset it, the car was dead as a dodo. I tried the ignition and there was no power at all so I took the battery out (less than 1 month old) and put it on the charger and it showed that the battery was fully charged (as I expected) so it seems I have a major electrical fault somewhere. As it is too dark for me to check right now I will have to wait until morning but aside from checking the fuses does anyone have any suggestions of what I should check?

I am a little pissed with myself in that I cannot remember if I unlocked the car first to open the bonnet to disable the siren or if the door was unlocked...
by that i mean I am unsure if the alarm was triggered by the power cutting out (the alarm triggers is someone removes the battery) or if the alarm was triggered by someone breaking in and screwing something up.

Initial inspection via torch showed no signs of forced entry or damage so my thoughts are it is most likely a fuse or something.

any help/suggestions would be welcome

SLYDIT
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Post by SLYDIT » Mon Jun 24, 2013 8:48 pm

sounds like your alarm has died and the immobiliser is stopping it from starting. sometimes if a battery is REALLY REALLY dead it will show as being charged on a battery charger funnily enough. only a multimeter will tell you for sure.
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MrGrey
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Post by MrGrey » Wed Jun 26, 2013 11:52 am

well, on monday night when I took the battery out it showed as charged when I initially took it out. The next day I connected it again to get a second opinion and it said that it wasn't charged..... soooooo 12 or so hours later it was charged and I just plugged it back in and things seem to be ok.

I guess I just ran the battery too low :(

To avoid this in future, I have ordered one of these:
http://www.ebay.com/itm/110758259352?ss ... 1497.l2649

now heres another question.... from what I have read, a full battery should read about 12.8v and a flat battery should read about 12.1v so, if I was to keep an eye on my levels and make sure I recharge it when it gets to around the 12.3v mark I should be ok in the future?.

-=edit=- the values I am using are from this:
http://www.wikihow.com/Check-a-Car-Battery

GRUVBB
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Post by GRUVBB » Sat Jun 29, 2013 7:39 am

If a battery is flat the voltage can read as if it should be healthy. The test is when a load is put on to it. The voltage will drop at this stage. Ohms law is P (power) = V (volts) x I (current/amps). The sitting voltage may appear ok until a load comes on. A true status test places a bank of resistance across the battery to test. Once the current tries to run from the battery the voltage falls as he power can not be delivered. If you leave a multi meter connected while trying to crank the motor you can see how the volts are affected. I realise that if an immobiliser is connected this may impede the starter circuit. If the battery is disconnected from vehicle a load can be wired across the terminals. Sometimes its best to take it o someone who has the test gear and appropriate knowledge for testing as shorting out a healthy battery can have devastating results. Difficult if the car wont start tho as those batteries are heavy to carry.

MrGrey
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Post by MrGrey » Fri Jul 12, 2013 10:46 am

ok so rather than starting a new thread, I figured I would resurrect this thread with a new oddity.

-= nouveau bizarrerie =-

ok, so I hopped in my car this morning and started her up. The engine and stereo were working fine as per normal. I then pressed the electric window button and nothing happened..... tried the passenger window button.... nothing.

ok, this is mildly concerning...

So I tried the window wipers ... nothing.

by this point I am suspecting a fuse has blown or something like that so I try the air conditioner. I initially couldn't hear if it was going or not so I gave the fan dial a twist and it worked ok...... and then everything else (windows, wipers) started working normally.

Has anyone else experienced this? was it caused by the coldness of the morning? is there any preventative maintenance I could do to avoid this happening in the future?

thanks for your input and suggestions :)

chris
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Post by chris » Fri Jul 12, 2013 10:54 am

Ha!

Mx5s always always have crazy issues.

That is a very strange one, I originally wanted to say your window switch was phucked.

However I now think a fuse could possibly be loose..
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Post by NicF » Fri Jul 12, 2013 11:41 am

Be glad you don't drive a BMW...

I was driving to work in mine this morning and for some unknown reason it decided to do a self test of every light bulb in the car. Startled the shizz out of me.
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GRUVBB
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Electrical problems

Post by GRUVBB » Fri Jul 12, 2013 7:47 pm

Sounds like a loose connection somewhere. Start at the fuse box and work back. You know the circuits that are functioning so look at the suspect ones. Check for corrosion/ high resistance points on connectors and fuse links. Check earthing points. Any sign of corrosion then clean them and add some contact cleaner or crc wd40 etc. if you have a multimeter check battery voltage then voltage at feed side of fuses then load side etc and make sure no significant volt drop as tou go down the circuits.

GRUVBB
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Electrical problems

Post by GRUVBB » Fri Jul 12, 2013 7:48 pm

Sounds like a loose connection somewhere. Start at the fuse box and work back. You know the circuits that are functioning so look at the suspect ones. Check for corrosion/ high resistance points on connectors and fuse links. Check earthing points. Any sign of corrosion then clean them and add some contact cleaner or crc wd40 etc. if you have a multimeter check battery voltage then voltage at feed side of fuses then load side etc and make sure no significant volt drop as tou go down the circuits.

GRUVBB
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Electrical

Post by GRUVBB » Fri Jul 12, 2013 7:59 pm

Just looked at wiring diagram. Wipers have own fuse and windows on another. Look at the connections in fuse box area for starters would be my initial advice

SLYDIT
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Post by SLYDIT » Fri Jul 12, 2013 8:05 pm

remove the grounds on the shelf under the wiper motor and give them a good clean. you may even have to cut the wires off that large white multi plug and use a new crimp lug before rescrewing it down.
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allenbak
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Post by allenbak » Thu Jan 09, 2014 3:23 pm

check connecters to rear lamps in boot if out click back in place, this problem happened to me after a panel repairer replaced both back tail light fittings with broken snap locks. It took a lot of playing around to isolate the problem, I had to do it myself. my temp fix was a short screwdriver to wedge the plug in on the side, stiil waiting for fix. :idea:

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