Turn signals stop working when headlights are on

[Kiwispider]

Drove my car for the first time in the dark and found my turn signals weren't working. Headlights off, turn signals ok. Headlights on, no turn signals.

Google search pointed to bad grounds or single filament bulbs in the front turn signals as the most likely causes. I've checked front bulbs are double filament and function properly as park lights when park/headlights are on, and as turn signals when park/headlights are off. Used a multimeter to check ground stars on both inside front fenders and got readings showing no resistance (or is the correct term impedance?). Checked the bulb housing inside both turn lights with the multimeter, again no resistance. So I think at least those grounds are good.

So that pretty much exhausted my knowledge of auto-electrics! In mild desperation I disconnected the feed wire to the parking lights, which unsurprisingly stopped the park lights working, but didn't solve the turn signal problem.

Please, can anyone suggest where to look next? Thanks in advance.

[RRoller123]

Could be that there is a voltage drop that is keeping the flasher unit from working when the headlights are on. There should be no direct wiring connection between headlights and flasher that I can think of that would cause this other than that. The flasher is behind the center section of the dash, I would pull it, clean and tighten the connections and see if that helps. Check the voltage getting to the flasher with headlights alternatively on and off, and see if there is a large difference. This is the first time I think we have heard of this one, probably a voltage problem.

There are a lot of critical connections that go through the Hazard Switch too, but I am not sure if that could be contributing to the problem. Also, check the ground pods on each inside front fender, and the one under the dash, driver's side. Clean and tighten the connections and maybe that will help.

[vandor]

I think on a Spider 2000 it's more likely that the rear taillight grounds are bad, or one of the ground connection to the or on the circuit board.

[Kiwispider]

Thanks guys, will try your sugestions. Since my last post I've discovered that the front turn signal has 11+ volts flowing to it when the park lights are turned on, even though the park and turns have separate feeds. I don't know what that signifies but I'm pretty sure it's not good!

Also checked hazards, they also stop working when park/headlights are turned on.

Hopefully these clues are a "lightbulb moment" (sorry, couldn't resist the pun) for someone who knows more about car electrics than me.

[Kiwispider]

And the prize goes to.....Csaba!

My panelbeater had removed the left rear tail light to do a small dent repair and had forgotten to reconnect the ground wire. Problem solved. I love this forum!!!