Message text written by "John Macartney"
>An interesting phenomenon. CG has developed a curious fault with her
right hand flasher. At anything above idle, both flashers work fine.
At idle, the right hand one stays on continuously. Bulbs are standard
types, contacts in bulb holder are clean as are the terminals, flasher
unit is new of correct type, flasher switch has been cleaned and no
evident breaks in the wires as far as I can see. Have checked earths
(grounds) to lamp units and these appear OK. Ideas? Can any UK lister
suggest brand names for a suitable anti-damp solution to spray all
contacts with during this unseasonally wet weather - apart from WD40?
John, my friend, as Dan Masters explained in his book on TR6 Electrics, the
flasher module used in the turn signal circuit is a current sensitive
device and will hold on steady the lamps IF the current is below a certain
threshold. This is the indication to the driver that something is awry.
In you case (as is the case in my TR6) the fault is not a burnt bulb but
rather a marginal situation where the current is just barely enough to
cause the flasher to flash at higher revs but as the voltage drops off at
tick-over the current also drops and it dips below the threshold causing
the behavour to which you are a witness.
One possible cause is dirty contacts causing higher than normal resistance
in this circuit and the resulting lower current. Another possibility is
older bulbs. Over time the tungsten in the bulb filiment will "boil" off
(actually, sublime is a more accurate term) and deposit on the inside
surface of the glass bulb. The result is that the filiment is now thinner
than it was when new and the current drawn by the bulb is lower as a
I recommend you try fitting new bulbs on the offending side in addition to
checking all power and ground connections for even though they may appear
to function they may not be up-to-snuff.
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