LED Lightbar as a turn signal
This can be done with three relays, single-pole, changeover type.







simulate this circuit &ndash; Schematic created using CircuitLab

Figure 1. Parking light and turn signals.

How it works:


With parking lights off the blue wire is energised. If either turn signal is switched on RLY2 or 3 will click on and off illuminating the lightbar on that side when the normally open (NO) contact is closed.
With parking lights on the orange wire is energised. Both lightbars will turn on. If either turn signal is switched on RLY2 or 3 will click on and off disconnecting the lightbar on that side when the normally closed (NC) contact is opened.








simulate this circuit

Figure 2. Timing diagram.

Note: It is important that the turn signal changes state immediately the switch is moved. This avoids the half-second or so delay that would occur if the turn signal logic is not inverted when the lights are on. This design achieves that requirement. 0.5 s at 72 kph is a travelling distance of 10 m when one car is stationary and 20 m if both are moving towards each other at that speed. That half-second can make a big difference in avoiding a crash.