I'm planning on installing led lighting under the dash but only want them on when the head lights are on, Whats the best / safest way of doing this. Thanks in advance.

 

Run a 12v source to them, and have a relay in the line. I'd suggest using the brown wire behind the headlight switch (running light wire) for powering the relay. Simple DPST or SPST relay will do you fine.

 

Me personally I would just mount them where you want them and wire them to either the battery or a 12v power source. If I was to do the battery I'd slap a "in line" fuse to be safe and then wire in a simple "on/off" switch somewhere discrete and nice.

 

I've bought enough used cars to see what people do to the factory wiring harnesses and what not. I also look at resell value and stuff like that so even if I want to mod it up I always try to leave factory wires alone as not to cause any issues down the road. Just my 2 cents

 

Same here. Even with the ute tails I wired up, if you wanted to revert back to factory, just use the factory plug. I use part of it without modifying it. You'll just have a chunk of metal missing behind the tails.

 

Too late for that, The previous owner spliced the lund visor lights into an existing wire, need to clean the mound of rubberized crap he has on these wires to see which one he spliced into.

 

Just a thought but an independent cut off switch might be nice to have on long drives, the added glow can cause some eye strain, it did for me anyway. Went down the same road your going and that's what I found to be the case at least with my old man eyes anyway.

 

These would be the simplest install.

12v Multicolored LED Strip

To wire them to your headlights, tap the headlight power wire to power a 12v cigarette lighter and stick the lights to the bottom of the dash.

 

I installed red, 8" Type S LED light strips under the dash and foot wells. Found them at Auto Zone. They come with a hard wire or 12V plug with on/off button. They also have many colors, sizes/lengths and programmable accessories that can create the atmosphere you're looking for.

I popped out the headlight switch and ran the wires off the brown (dash light) wire and the ground wire (white if I recall) with saddle connectors. Easy enough, no cutting wires and they dim with the dash light dimmer. No relays, resistors, everything off the dash fuse via the switch.

I used saddle connectors for 2 reasons. First you don't have a lot of wire that pulls through with the switch. Hard to splice into. Second it's in the dash, not exposed to the weather so no rust or corrosion.
This is under the passenger side and center of the dash. I used 3M 2 sided tape to mount under the heater box and to a piece of angled aluminum which I drilled out and secured with an existing dash screw.



This is the driver side. I used a short piece of angled aluminum to mount the light strip at the hood release. Top left you can see the light strip in the photo but isn't visible while driving.

 

I was going to chime in like RCB just stated and say the same thing. The headlight switch wiring or any courtesy light (ash tray or power area), and then tap to those with either good (red) taps or solder in there. The pull off LED strips is so little that a relay is not needed or used. It would be just plain overkill for the milliwatts the led's would require.