Electrics: Strange intermittent electrical problem

[Simon J]

OK, some further info. I discovered that once the car is warmed up I can make this odd fault happen by holding up the driver's or passenger's window lifter button! It doesn't seem to happen with the rear window buttons. But only when stationary or moving slowly.

Any further ideas, guys?

[Toplights]

PM Chris Rogers allways helpful.

[Simon J]

I thought that it would be helpful to post the solution to this conundrum. The problem had been getting worse and even flashing the main beam headlights would trigger it so I took the C70 to my local auto electrical shop in Belfast, Greenaway's on the Beersbridge Road. Since the problem could now be easily demonstrated by flashing the lights or operating the window switches, these clever guys had it tracked down in a couple of hours.

The first thing they noticed when running checks on it was that the alternator didn't seem to be giving a consistent charge although apparently sufficient to keep the battery charged. Their first thought was that the alternator would need to be replaced (I can't imagine how much that would cost!) but they checked out the wiring and found that the cable to the positive terminal on the battery was getting warm to the touch and they could detect some movement in it. Wriggling the cable made the charging rate at the battery fluctuate. On further examination they found that the joint where the cable connected to the battery terminal was poor and this was the cause of the fluctuating charging. They remade the connection but still reckoned that the ABS sensor might also be at fault as its warning light was one of the ones coming on. But further tests showed it to be fine so the problem was much simpler than was thought - a poor joint causing variable charging which was only a problem at low revs, i.e. on tickover or in slow moving traffic, as once the revs came up the charge rate was sufficient to overcome the poor connection. Hence the fact that the problem never occurred when driving on the pen road - only when stationary or at slow speed

The explanation for the odd behaviour resulting from the poor connection seems to be that if the charge rate dropped at idle because of the poor connection then the voltage fell slightly and one or more of the relays simply dropped out, to pop back into place once the charge rate came back again.

I've only driven a few miles since the fix, so I guess it could still come back, but so far so good.

Who'd have thunk it? A bad connection on the battery cable!

So anyone over here in Norn Iron in the Belfast area could do no better than give Greenaway's a call if you've got any electrical problem - http://www.greenawayelectrics.co.uk/
No connection other than as a VERY satisfied customer.

[Toplights]

Thanks for posting the solution.

[bob865349]

Try this website for wiring diagrams.
http://www.volvowiringdiagrams.com/
Regards