Why is there a glimmer from my ignition
Dave Hedger posted a query on the V8BB about a glimmer from the non
charging light on the dashboard of his RV8 and sought fellow members'
help. (Jan 08)
Dave Hedger was out in his RV8 on a run on Boxing Day
(hood down and glorious) and for the first time for a long time it
got dark before I got home. Apart from the almost total absence of
instrument lighting - something that I have been told is to be expected
- I noticed that the charge light in the dashboard had the mearest
glow - to be seen whilst on the country lanes - can't be seen where
there are street lights! I am not suffering from any lack of charge
to the battery. Is this an impending sign of doom or is it possibly
a slightly resistive earth connection somewhere? Any thoughts would
be gratefully received.
Nigel Melbert responded: I had the same problem with my MGBGTV8
when the ignition light was seen to be on when through France at night
but it did not cause a problem. The alternator and battery were all
in good order, the circuits were checked with the correct current
flow from the alternator and battery to the ignition light. The problem
turned out to be the bulb in the ignition light having the incorrect
resistance. I had to try two or three different bulbs to find the
correct one. No problems since. Incidentally the dim instrument lights
can be solved by fitting halogen bulbs.
Brian Moyse with an RV8 noted: On dim instrument lighting,
an improvement can often be made just by replacing bulbs at say four
to five year intervals. Instrument lighting bulbs rarely blow, particularly
when operated at reduced voltage with a panel light dimmer. They do
however, over the years, suffer a build up of a black deposit on the
inside of the glass envelope, presumably an emission from the tungsten
filament, which significantly reduces light output. The same applies
to all tungsten filament bulbs, so it's worth having a periodic check
of all the external lighting - for example side/tail lights as well
to ensure maximum visibility.
warning light and dimmer on an MGBGTV8. (Source: MGBGTV8 Driver's
Chris Hunt Cook who is a regular participant with his MGB Roadster
prepared in road rallies, needs to see his instruments at night added:
I agree that the bulbs blacken with time but also the panel light
dimmer seems to deteriorate and give much more resistance in any position,
and it is expensive to replace. You could try just shorting it out
with a short piece of wire - that made my instruments readable at
night and even in that improved state the panel lights are hardly
bright enough to need dimming anyway.
Another thing to check with the ignition light is that light from
the panel lamp is not leaking across into it producing a slight red
glow. Try turning the lights off (having parked of course!) and see
if that makes any difference to the glow from the ignition light.
added: As I recall, if you take out the panel light dimmer, you can
see the wire wound rheostat/contact wiper. An increase in resistance
is most likely due to a build up of dirt in the rheostat, which may
be removed using an aerosol electrical contact cleaner or similar.
Then work the dimmer to and fro so that the wiper contact cleans the
surface contact patch of the rheostat winding.
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