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MG MGB Technical - Electrical Pulsating Short

I wrote last fall about an electrical problem I was having that drained my battery. It was suggested at that time, to put a test light between the unhooked negative battery terminal and the negative battery cable.
This worked great and I was able to pull fuse’s and wires until the test light went out.
It turned out to be one of the purple/white wires for the interior door lights which had come loose and making contact with the top of the tape deck.
So I fixed that problem and then tested again. Now the test light flash’s once brightly and then in 1 second pulses but so faintly it is almost invisible.
I can just ignore it and say it’s the clock in the tape deck but what would cause the bright flash?
It is like a storage of power.
Any one able to shed any light on something like that.

Bruce
MGBV81

As a guess, you are discharging a capacitor with the light, then the capacitor is recharged through a resistor, which is why subsequent "flashes" are weak. If the pulse is in fact a one second interval, a clock would be a good bet. I'm sure this is not a technically complete explanation, but it seems a good first sortie.

FRM
FR Millmore

And if that seems correct, couldn't it be verified by disconnecting the tape deck? Alternatively, is there a capacitor elsewhere in the car that could be disconnected?

Charley
C R Huff

Thanks guys.
If I disconnect the taped deck the flashing stops of course.
It makes sence that there is a is some type of capacitor which store energy to operate the clock??
Problem solved.
Thanks

Bruce
MGBV81

I'm sure capacitors are involved somewhere, but it will be electronics. If the player has a clock then that is more likely to be digital and take a tiny steady current. Analogue clocks that 'tick' at one second intervals will take a 1 sec pulse. Others have a 'conventional' movement that is periodically wound up by a motor, but only once every 20 secs or so. Could be an 'anti-theft' LED on the radio/CD player that pulses, some of those go at 1 sec on 1 sec off, others at brief 1 sec pulses.

Whichever, the drain is microscopic and can be ignored.
PaulH Solihull

This thread was discussed between 09/03/2011 and 11/03/2011

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