Indicator tell tale with hazards?

zeaphod · Dec 22, 2014

Hi all. An odd fault popped up at the weekend - no indicator tell tale on the dash, indicators themselves working fine. Bulb OK. As I was working through the problem (which just went away) it looks like there is voltage on both sides (GR and GW) of the tell tale when the hazards are used, so the dash tell tale should not work when the hazards are on. can anyone confirm this, i.e. your dash indicator tell tale doesn't come on with the hazards? Ta
Oh, it's an 1985 90".

Kwakerman · Dec 22, 2014

The trailer warning light flashes on mine with the hazards on, the indicator light doesn't. The way most indicator warning lights work is that one contact of the bulb is connected to the left indicators and the other to the right. in normal operation the bulb uses the the earth return through the opposite lights . i.e if you have the left indicator on then the 12v from the indicator goes to one side of the warning bulb, the other side of the bulb is effectively earthed by the right indicator bulbs (the right indicators don't light up because of the internal resistance of the indicator lamp). In your case I would expect 12v on each side of the warning light with the hazards on as both the left and right indicators are supplying 12v to each side of the bulb. As there is no potential difference over the indicator warning bulb it wont light.

zeaphod · Dec 22, 2014

Kwakerman said:
The trailer warning light flashes on mine with the hazards on, the indicator light doesn't. The way most indicator warning lights work is that one contact of the bulb is connected to the left indicators and the other to the right. in normal operation the bulb uses the the earth return through the opposite lights . i.e if you have the left indicator on then the 12v from the indicator goes to one side of the warning bulb, the other side of the bulb is effectively earthed by the right indicator bulbs (the right indicators don't light up because of the internal resistance of the indicator lamp). In your case I would expect 12v on each side of the warning light with the hazards on as both the left and right indicators are supplying 12v to each side of the bulb. As there is no potential difference over the indicator warning bulb it wont light.

Thanks! Makes sense - and explains why when I fitted 4 led indicator bulbs there was a bit of leakage through the tell tale bulb which dimly lit the "off" side in time with the on side. Should have bought the proper LED units with a built in resistor, instead of the "not recommended for on-road" ones.

Indicator tell tale with hazards?

zeaphod

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Kwakerman

Well-Known Member

zeaphod

Well-Known Member

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