12 volt relay, LED's

Hello.

I've looked through the forums, and I can't find an answer in the other posts that I feel specifically helps me. I have a 2006 Dodge Ram quad cab. I have two main questions.

I have several LED's that are already ran under the dash, and the seats to illuminate the floor, hooked up to a toggle switch, with a 12v constant. What I want is when I turn my headlights on/off, the LED's turn on/off. Also, when I unlock/open my doors, I want the LED's to turn on, and fade out with the overhead lights. I understand that to power the LED's from two sources, I'll need to use a relay. Of course I'll have to determine the wires in my truck that I'll need to use for each one. How I think I'm supposed to connect the relay is: 30 to LED's, 85 to Ground, 87a to overhead lights, and 86,87 to headlight switch. If I understand correctly, that should allow the LED's to come on when I open the doors, they'll fade out with the overhead lights when I shut my doors, and they'll come on when I turn on my headlights. If this is right, what type of relay do I need to use? I have no experience with relays and which one I need.

Second, I want to be able to dim the LED's, preferably with the dimmer that controls the gauge cluster. Is there a way to do this? Perhaps the wire that I need to connect that will turn on my LED's when the headlight switch is on is the same switch that will also dim them?

~J

Also, something I just thought about that goes with my first question about which relay, if my diagram is correct. How is the OHM rating of the relay going to affect the output to my LED's? How do I recalculate those values? The strings of LEDs I already have wired are hooked up with resistors already and hooked up directly to the battery via switch.

Dash lights come on with the parking lights so if that's alright then you can substitute it for the headlights wire.
You wiring is fine and the relay shouldn't affect the resistence as that of what have that you would need to change what you have.

Ok. I guess now i need to figure out how to connect the one side to the dash lights where they will come in and dim. And find the wire that i need for the overhead lights. Any suggestions to where i can find this information? Also, what should i look for in a relay?

I just thought of another question as well. Would it be a good idea to include diodes in my wires somewhere? Like on each wire running from each power source to the relay?

No diodes should be needed for lights when using a relay as you are.
And any standard 5 pin 30/40 amp 12v automotive relay will work even the mini relays 10/20 amp are rated high enough to do what you need. You can check the wiring list on this website also www.readyremote.com www.buldogsecurity.com and www.techservices.audiovox.com (free sign-up required).
Get as many wiring sheets to cross reference as needed so you know what you are looking for.

Okay, great, thank you so much. That should be a big help. I will check them out. If any 12v SPDT 5 pin will work, that will help make it easier for me to find one. Also, I've noticed that some come with a harness or plug with wire leads attached. Is it better to use one of those, or just solder directly to the relay?

You can use regular crimp on spades if you dont want to buy the harnesses. If you not in a hurry to get them ebay has them cheap. Or a local salavage yard out of any wrecked vehicle. Most of the newer cars use the OMRON MINI RELAYS.

Okay thanks. I went out and picked up a 30a 12v relay today from O'Reilly's auto. I did my own test to see if it would physically work the way I drew out my schematic by using batteries to power the circuits, and it will. I found out the it takes at least 12v to switch the coil, but will pass through any amount of voltage on pins 87 and 87a. Now I just have to pull out the headlight switch on my truck and determine which pins do what I want. I know what the pins are based on a wiring diagram I found, but not what they do.

DMM black to ground and red probe the wires while working the dimmer with the parking lights on to find the voltage changing with the movement of the dimmer.

You'll need a PWM to dim the LEDs linearly, older variable resistor types won't work (linearly) but most modern dimmers are PWM even for bulbs.