strange surges in electrics

[Dominic]

Hi folks
A while back I reported that the windscreen wipers sometimes of their own accord suddenly increase speed. The normal speed is pretty much the same as it was on my previous Morris, so I am sure they are speeding up occasionally rather than slowing down a lot of the time.
I have now noticed, since having to use the headlights in these darker evenings, that the light output suddenly increases as if the full beam has switched on, though it is not full beam, as the area lit by the headlights remains constant. Also the blue full beam light doesn't illuminate. (Full beam switches on as it should, but I have not seen any power surges there as I rarely have the opportunity to use full beam)
This is noticed when driving, after a while the light is suddenly brighter for a few minutes, then it dims back to what looks pretty normal for a while. The car has an alternator conversion, that a previous owner installed. Also halogen lights.
Please can anyone advise me where (and what) I should check?
I'm a little concerned as I don't want to be suddenly in the position of no lights at all on a dark night, nor do I want to fry anything!
There are no extra electrical items added except a power supply for occasional sat nav use. (a ciggie lighter)
Thanks for any help, which will be gratefully received!
Dom.

[bmcecosse]

A poor battery connection could do this -if the alternator loses contact with the battery the volts can rise considerably - and will indeed blow the bulbs and damage the alternator. So - check the battery connections - and the earth connection beside the battery tray - and the earth cable at the gearbox mount. Your high beam warning is a different problem - very possibly the bulb holder has simply fallen out of the speedo.

[Dominic]

Thanks for the reply Roy.
I actually meant that the blue light didn't come on when the lights brightened - my initial thought was that somehow both elements were being lit! It lights up when on full beam no problem.
I'll check all the connections this weekend. When I was tidying the car up, removing servo etc, I found there was an additional earth strap from the engine to the chassis, as well as the gearbox earth. Reckon it might be worth reinstating this?

[bmcecosse]

Absolutely - you can't have too many earths.......

[Roni]

Have a look at the alternator connector too. The same symptoms happened to mine when a big spade connector gave up.

[Dominic]

Solved the problem.
It was a poor earth between engine and chassis. For some reason there's not a strong electrical bond between gearbox and engine. I have therefore run an earth strap between the back plate and an engine mount. Lights stay brighter all the time and so far the wiper speed remains constant.
Thanks for your suggestions chaps!

[bmcecosse]

Hmmmmm - more likely to be poor earth strap at the rear of the gearbox - but never mind -your new strap is ideal and the problem is sorted!

[IslipMinor]

you can't have too many earths

Agreed. My son's MGB had an additional earth from one of the front engine mounts down to the front cross-member. The only problem is that the front cross-member is attached to the bodyshell via rubber mounts, so not very effective! Now goes fron the bulkhead to one of the gearbox bell housing bolts.