V40 power surging
 

Another problem my V40 has - voltage surging!

Only happens when warm or hot. I'll be driving along happily and a load of warning lights come on on the dash - parking brake, info, SRS, washer bottle level, etc. The headlights become brighter, the fan runs faster, the wipers run faster, the dash lights up like a Christmas tree, and sometimes the radio turns off, presumably to protect itself.

My feeling on this is the voltage regulator is on its way out - the alternator is obviously providing voltage, but the regulator can't keep it at 14v. Does this sound right?

If so, would this item on eBay do the job? And if so, where do I fit it? There looks to be a cover on the back of the alternator where the wires are attached; presumably I remove this and I'll find it inside, bolted to the back of the alternator?

http://www.firestryke.xyz/VOC/alternator.jpg

Any help appreciated!

The green plug shouldn't be connected anywhere?

First off I would check all your battery leads and earth leads for loose or bad connections. As a matter of course I would take the battery leads off and brighten up the terminals and clamps with some emery paper.
Then if you have a multimeter you can check the charging voltage at the battery.
Also check the battery is good as when they are near death they can produce some weird effects.
That done then I would disconnect the battery leads (both to be certain and at the very least the negative lead) and then disconnect the alternator leads and remove that cover so you can get a part number off the old regulator/brush holder. Unless you are 100% certain of the alternator you have I wouldn't rely on an online parts search without the original part numbers off the alternator/regulator.
It may be possible to do the work on the alternator without removing it. I don't know how much room there is to get access.

I figured the green plug connected to something that would have mounted to the bracket at the top of the picture. It was covered in black gunk and wasn't even slightly green until I wiped that off. It doesn't connect to the alternator tho - it's way too short.

I was thinking I would have to take the old one off. I think it can be done without the alternator coming off but it's very, very tight for space and it might be easier to just remove the alternator first.

Battery is fairly new, terminals are good (I checked them over when fitting the battery). Charging voltage is also good at idle, but as the fault is only reproducible when the vehicle is being driven, the only easy way I'm going to be able to get a voltage reading is from the cigarette lighter or radio connections. So maybe that's next on the troubleshooting list.

Green plug; Air-conditioning maybe?

Alternator; as said, put a meter on the battery. If the regulator is faulty you'll see it. When the same thing happened my Cavalier (first clue was brightening headlamps), the voltage was erratic and peaking at 32v, and it very quickly fried the battery. So don't delay.

The alternator is simple to remove. Slacken the belt with an 11mm spanner on the tensioner wheel, wiggle the belt off, then it simply unbolts.

Better take off the alternator and bring it to a technician who knows how to repair becouse if the regulater is bad the bearings and cupper slide rings inside will have their best time.If inside a diode is death you can not find it with a voltmeter becouse a alternator is a tri phase device and you will not be able to see such things on your meter.
When bussy check the wires + and - for bad connections /corrosion and hope there is nothing fried elsewhere .

as Loely said, I would take the alternator to a technician and have it checked. I think I can do everything in a car, but the alternator is kinda a black magic box for me, so I take it to the people that knows how to work with them and have it fixed.

Follow-up
 

Just following up on this for anyone who comes across this thread...

Turned out the alternator fitted was some generic aftermarket one and I couldn't get a replacement voltage regulator for it. I picked up a genuine Volvo alternator with regulator second hand from eBay, fitted it with the aid of a crowbar (let's just say the aftermarket one didn't fit properly so hadn't done the mountings any favours) and job done, problem gone. :)

Thanks for everyone's input on this thread!