Ignition light glimmering

[kenton]

Been tinkering..
So the light glimmers with the same brightness regardless of engine revs, headlights on etc.
A direct earth from the alternator casing to the battery changes nothing.
Swapped withthe brake warning light, no change.
As I had some spare dash lights i put a second bulb in series, that fixed it.
So it seems a higher wattage bulb is needed....or I could leave the second one wired in behind the dash
Not my usual standard of fixes but it works.
I have a few questions.
1 Will this cause any issues?
2 I assume the cable will take the extra load?
3 should the bulbs be in series or parallel?
Thanks
K

[andyf]

By adding the bulb in series you have increased the resistance which will reduce the current in the circuit. I would say that you need a lower wattage bulb or possibly a series resistor for a proper fix.

[ChrisS]

For whatever reason, there is a voltage difference between the main alternator output and the regulator bootstrap input where the warning lamp connects. There are a few ways you could resolve this, two bulbs as you've discovered, I suspect a lower wattage bulb would actually glow brighter and you'd risk it not being able to carry the required bootstrap current so could keep popping. Try a single higher wattage one?

It would be interesting to know which side is higher than the other though, ignition switched 12v side or alternator side. Could help diagnosis.

[andyf]

A lower wattage bulb would have a higher resistance because it draws less current for the same voltage.

[Hammy]

I had something like that, just before I lost all electrics and we had to coast into a gap betweent the cones on the run down to the Dartfort toll booths during a Friday rush hour, with the sun behind us - hence why the glimmering hadn't been noticed until I said "what bad thing can happen ......" Oh. Mark will remember that, we were due at his ready for a trip to Ypres the next day. He kindly came out to supervise Paul and the RAC man. Alternator had shaken itself to bits inside, due to the inevitable Tiger dodgy alternator bracket scenario.

You out of hibernation Linda? PM'd you a while back and thought you may have sold up and moved on...