Looking for positive trigger wire for relay

I installed under glow lights under running boards and I would light to trigger them on dome light circuit. I know most lighting is switched on negative wires. Has anyone found a positive wire that comes on with dome lights?

 

you can trigger a relay off a switched negative.

https://www.youtube.com/watch?v=QAD8vDHTbzo

 

Personally, I wouldn’t mess around with using a relay on the dome light circuit, I tried doing something like that for a power supply to a dash cam and it even affected the DRL’s.

You will need to keep it separate like the post above, and if you want your lights to slowly dim when the dome lights turn on and off, you’re better off using a different method. How good are you with electronics?

 

Power them like the OEM cargo bed circuit.
Use battery fused to relay pins 85 & 30(+)
87 to added lights (+)
86 to cargo switch connector violet wire. (-)

 

The lights stay on with purple wire. Should I try white with black stripe? That's a ground but not chassis ground on diagram.

 

Are you testing it with the door opened?

 

Thanks Again so much.

 

No pics for us?

 

Makes getting out so much easier.

 

Where did you place them? pinch weld of body?

 

Under side rails.

 

That's a nice truck! And the lighting is really cool!