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MG MGB Technical - Mr Miyagi Says - 'Lights on, Tach off'

Hi guys,

anyone remember the film the Karate Kid, Mr Miyagi says "Wax on, Wax off". Well i have similar problem, although it envolves no wax! Every time i switch on the lights on my 71 BGT the tachometer dies. Switch them back off & it comes back to life. Any ideas where i should start looking.

I am not sure if this is related but my fuel pump sometimes seems to stop pumping. This happens randomly & not very often. I am going to start by checking all the electrical connections to the pump, but if anyone has any other ideas i would be glad to hear them

Cheers

Scott
Scott Ralph

Scott, it may be a bad ground on the lights. When you click them on, it grounds through the tach (the tach feed on your car is, I believe, negative). The current coming down the line throws the tach all outta whack. I would try re-earthing the lights (just hook up a grounding wire to the black wires coming back from the lights).
Dan Fields

Bad ground to the tach. With the lights off the tach grounds through the lights. With the lights on there is no ground left for the tach. There should be a black ground wire secured under one of the thumb-wheels that secures each gauge in the dash.
Paul Hunt

Thanks guys,

is was a bad ground, one of the thumb wheels on the back of the tach had worked loose. Tightened it up & all working again.

If only all problems where as easy to fix as this!

Cheers

Scott
Scott Ralph

Don't forget the fuel pump!!! It sucks fixing it on the side of the road! It will usually go @ night in the rain!!
Check the connections, but also suspect the points. It has been my experience that a SU fuel pump is good for about 5 years before the points start to go. I switched to the new SU with the electronic points, so far so good.
Robert Dougherty

This thread was discussed between 20/05/2002 and 22/05/2002

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