Weird wiring!!!!!!!

[Radders]

Ok, strange one this........

While out in my Mk2 estate tonight I suddenly noticed that all of my dashboard lights had gone really dim and that the voltmeter was reading below 11 volts. The wipers also slowed right up and the indicators stopped  flashing when I needed to indicate. Obvious signs of battery or alternator failure I thought.........

However, when I slowed down and took my foot off the gas, the voltmeter came back up, the dashboard lights became bright again and everything started working as it should. When I started accelerating again, the u/s alternator symptoms came back!

Once I got home, I also noticed that when  you rev the engine, the headlights flicker and go dim momentarily?????

Any ideas whats causing this anyone?  

[Alex]

Fan belt loose/worn and slipping under load?

[Nick Jones]

^^^ WHS^^^

Nick

[TedTaylor]

Quoting Alan Chatterton on the Register Forum:
"Check your earth strap........... quickly!
It's loose, missing,broken or needs the connections cleaning.
It changes when you rev the engine, as it connects, then doesn't, and its very probably earthing via the throttle and choke cables!"


What can happen is that because these act as the earth connection, when you start to draw a lot of current (full headlights or starter motor) they get very hot and can seize up.
Had this on a Range Rover with starting problems but did not realise what the fault was until the auto box selector cable seized because the nylon liner had melted ........ and they are expensive to replace :shock:

Ted

[mikeyb]

yeah first thing I would look at are earths, closely followed by alternator power wiring and connections

[Radders]

Nick_Jones wrote:

^^^ WHS^^^

Nick

Eh? What does this mean????

[Nick Moore]

"What He Said", usually followed by arrows pointing towards the previous post. A harmless bit of forum flimflammery  ;)

[Steve Cureton]

1526 wrote:

... when you start to draw a lot of current (full headlights or starter motor) they get very hot and can seize up.

.. and can catch fire, so check them ASAP.

[Radders]

Just as an update to this......... The earth strap from the engine bock to the battery was fine. However a second earth strap also from the battery to the body had broken.

Once replaced, the car revved and drove fine with no loss of voltage.

Thanks to everyone who offered advice.   :)

[junkuser]

"The earth strap from the engine bock to the battery was fine."
If that was a woven type earth strap looks can be deceptive.
They can have loads of broken strands and still look OK.
Working on the Spit one evening in failing light I used the solenoid to start the engine and was surprised to see a fireworks display throughout the woven earth strap.
I had just finished replacing the needle valves in the carburetors to overcome flooding and the earth strap was below the rear carburetor.
Now have earth cable across back of engine from battery earth to bell housing.