Im installing a relay to run some emergency lights in my 2008 dakota. I need the power to be cut as soon as the truck shuts off. Where should I pull the switched power from? I tried using the fuse for the power windows but the relay doesn't open when the truck turns off.F

 

You could check whatever fuse the cigarette lighter is on, at least in mine that has no power when the truck is off. Best bet is to test a few with a multimeter (if you don't have one they're well worth having around, you can pick up a fairly decent one for not too much).

 

Heated leather seats is on fuse 58, even if you don't have heated seats it should be there. It's a 12v switched source. I used it for my electric fan, I think there's a 30a fuse in it.

 

You need 2 power sources, one for the low amp side (this is the side that activates the relay) and one for the high amp side (this is the side that feeds whatever you're using the relay for).

Pick a circuit that has power with the key in the ON or ACC position and use this to feed the low amp side of the relay through a switch, then depending on how many amps you need for the main power feed, you need to either pick a circuit that you can tap into, or you can add another small distribution box right onto the battery and hook up a line from this to feed your emergency lights or whatever.

Here's a picture of how a relay functions:

relay.jpg

Your low amp circuit is connected to pins 85 and 86 - 1 pin needs a +12 source (this is that circuit I mentioned earlier that becomes live with the key in the ON position - this would feed a switch, and the switch would feed pin 85 (or 86), the other pin would go to ground.

Your high amp normally-on relay position is what you get when you turn off the power to pins 85 & 86 - this is pin 30 and 87a and you won't use this combination.

The normally-off high amp pins are 30 and 87 and these are activated when you turn on your low amp switch. Pin 30 should be connected to the high amp +12 supply and pin 87 is then connected to your "thing" (emergency lights in your case) - don't forget to ground the "thing" to complete the circuit.

 

I Installed LED Strobes (White/Amber) on my 05, But mine are setup to stay on and Turn on/off when truck is off or on.
I ran my Switch power wire to my Fuse box and installed a "Add-A-Circuit" with a 7.5a Fuse (since its only a switch, a 5a would prob work to)

All you need to do is, If you dont need ur 12v Cig outlet to be On all the time. Is move the fuse in the Fuse box over 1/2 Slot sideways (Read Fuse box cover)
This will change your inside Cig outlet to ING or Constant Depends which way it is moved.

85 - Switched Power (After Switch)
86 - Ground
87 - To Emergency Lights (Dont forget to ground your lights)
30 - Power Feed
87a - Not ALL Relays have it, You could get a 4 Position Relay, not 5. I just capped the cable nicely so it cant Accidentally Short to anything. (I Suggest getting a 4 Position Relay for Safety)

EDIT: Also Add fuses
1. Switched Power Feed (Before Switch)
2. Relay Power Feed
3. Relay Power Out To Emergency Lights


Heres the Thread on the wiring Harness I made up for my truck (Strobe Lights, 55w Front Lights, 55w Rear Lights, Rear Camera, EFan (Future) and a Spare)
https://dodgeforum.com/forum/3rd-gen...ts-dakota.html

 

Thanks guys, I'm going to give it a shot today. I had the lights wired in a way that they could be on/off with the car off but now I have a scanner installed that would be a constant drain.