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Rav4 D4D 2005 Problem- Replaced Alternator and Battery but still low voltage, also Rear Fog lights won't work.....help please!


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Hi, I've just had my car in for MOT and £710 later (brakes, tyre, new alternator) the mechanic still can't pass the car as the rear fog light won't come on (he tried changing bulb but says there's no power there. The dash light does come on when switched on- I have read that it could be an issue in the trailer connection point, but can't unscrew it as the screws are so corroded.......is there a way of measuring voltage across 2 of those pins (I have a multi meter)?

2nd part of this, which I not sure if connected but doesn't feel like it is, is that after changing the alternator, the voltage at the Battery is still quite low (c.12.5v). Mechanic says he has checked all fuses and can't work out why it would be low. The warning lights that I had when alternator was shot (Battery and water in fuel lights) do still come on......but disappear if revs are 1,500 or over!

Any help or guidance would be very very much appreciated. I have it booked in to an auto electricians next week, but want to make sure there's not something I can test/try before having to fork out more £ (that I really haven't got) for it.

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How old is the Battery? They have been known to die after three years or last 7 years, depending on use and care.

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2 minutes ago, Dippy said:

How old is the battery? They have been known to die after three years or last 7 years, depending on use and care.

I've gone through a Battery a year for the past 3 years (which is what led to the alternator being tested). This one is brand new.

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From what you have said my money would be on corroded connection points at the trailer socket which is known to cause issues anyway. I would buy a new socket, lead and replace. Just drill the old screws out. Any corrosion there to earth will cause all sorts of aggro.

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Thanks satts. So the 2 issues could well be connected- the dodgy trailer connector could be playing havoc with the alternator?

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Your car is also of an age where poor earth connections can cause issues (usually hot start but other issues have been posted). I'd be inclined to clean the earthing cable connections - a few threads down you'll see my notes on doing that. There's a chance it will help but certainly can't do any harm.

 

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my dad had a similar issue in phantom drain on a Battery on his Jag..turned out it was the towbar connections causing the issue... took multiple motor electricians to diagnose! 

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Thanks for the responses. I'll cleanup the negative connections and see what I can do with the trailer connection......worst case I'll mention all the info to the auto electrician if it ends up there.

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The alternator is probably ok its just that any shorts to earth or back feeds from corroded connections in the trailer socket may stop the alternator from charging the Battery. A Battery per year isn't getting to the root cause of your problem and just masking it temporarily. Change the socket anyway for piece of mind and to eliminate it. Should only be a few pounds..

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Yeah, I'm starting to regret forking out for the new alternator! Though I suppose it does no harm and future proofs it a little while longer (once I get to the bottom of the actual issue).

I managed to get out with my multimeter today and test the rear fog- the mechanic said there was no power, but I read 11.8v testing the actual socket........I had been wiggling cables around and spraying electrical cleaner into the trailer connectors (and any other connectors I could find), so maybe that's realigned/cleaned up something (assuming he tested correctly in the first place).

Will continue the search for the alternator problem tomorrow, though from what you've said it made me think that someone kicked my passenger wing mirror off a few years ago and I just reattached it........but the wires were completely sheered; maybe that's what's been causing (or at least adding to) the issue. It would definitely tie in timing-wise to when I started having to replace batteries.

 

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If the wing mirror wires were sheered and you didn't unplug it from the loom (this would have involved removing the door trim) then that would most certainly need resolving first and foremost. Remove the door card, unplug the wing mirror from the main wiring loom and see if you get your fog light back. All simple stuff you can rule out without involving specialists. You could try just pulling the fuse for the wing mirrors see if that changes anything but it may take out other stuff as well...

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OK, so got out today and disconnected the knackered wing mirror- no change, but at least it's ruled out now.

I also cleaned up the negative connections (no change) and then pulled every fuse, one at a time, while monitoring the voltage across the Battery.....no fuses altered the voltage (other than very slight increases which I'm assuming is down to less draw).

Lastly, my new bulb for the rear fog light still didn't work. Getting voltage (11v) at the bulb socket, but not one bulb lights when put in. I tried cleaning the socket a bit with some electrical cleaner and fine sand paper in case it just wasn't getting a nice connection.....but no joy. Safe to say I'm now stumped!

 

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Weird, I've never worked on the fog light but I think the following is possible; I'd try running a +ve and -ve feed to the bulb direct from the Battery just to make sure something happens remove the car completely from the equation.

If the above works I would then try one at a time ie run a wire from the +ve on the Battery direct to the bulb and rely on the car negative for the return and see if it lights up. Then I'd flip it round and bypass the car car on the negative side.

Good luck!

 

 

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11v is too low. You have a bad connection somewhere so although you have 11v, a bad earth in the light circuit is dragging the voltage down.

Try swapping the light clusters over or buying a second hand one to test. Don't know how easy that is on your vehicle...

https://www.ebay.co.uk/itm/Toyota-RAV4-XA20-MK2-5-Door-Rear-Left-Passenger-Light-Cluster-Assembly/154281025712?hash=item23ebdda0b0:g:8gkAAOSwubRf9x3N

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Hopefully of use - when my LandCruiser had its MOT in 2018 it failed because the rear foglights weren’t working (embarrassed!). The tester at the Toyota main dealer in Preston sorted it straight away by disconnecting the tow-bar electrics. I no longer used the tow-bar so didn’t think about it much, but it suggests that tow electrics can affect things, maybe even if you don’t actually have a connection to them. 

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Update- got the rear fog sorted.....it was indeed the trailer connection causing the issue, so had it unwired.

Alternator problem still there though. Auto electrician tested the wiring and came to the conclusion it's a bad alternator (he said what's going to the alternator looks good, but then there's nothing coming out of it to charge the battery). Not sure the first garage believe it's the alternator, but they've said they'll change it out anyway and see.

Fingers crossed!

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The alternator has been replaced already hasn't it? I would get them to look at the plug it could have burnt out pins if the old alternator / regulator failed.

Don't keep replacing batteries and alternators its an expensive hobby! 🙂

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Yes, it was replaced last week but wasn't charging the Battery.

The auto elec tested the "4 point plug on the back of alt, all leads and all fuses those leads go to". He said everything at the 4 point is fine, but there's less voltage coming out of the alternator.

None of them have a clue why the Battery, Oil and water in fuel light would come on until revs are over 1,500, but it's back with the first garage to complete MOT and swap the new alternator back out.

Will update once they (hopefully!) get to the bottom of it.

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