Ok, this is probably a stupid question, but I'm getting frustrated. I'm a trying to install a simple aftermarket gauge that will have power only when in "run" mode or vehicle operating. I bought an inline fuse set up, looked in my fuse cluster and picked several locations that fit this...Back up lights, spare fuse slots, etc. Each time, the gauge does not operate unless in a "hot" fuse, such as Pedal adjusters?? I know the gauge is hooked up correctly and functions but why do all of my fuses seem "hot"? I really don't want to splice somewhere but surely guys are hooking up various gauges somehow.

BTW, the truck is bone stock and an '04 hemi 2500.

Thanks!

 

You need to use a test light or a volt meter to check and test for the right fuse so yuo dont keep guessing. On a side note, you can tie it into the cig lighter.

 

could be that they need to be powered on through the ecu via Dealer program or that they simply aren't powered at the box.
I personally run seperate wires to the battery and hook up like that. This way for me the dealer cannot deny wiring related warranty issu'es. For you I know you aren't concerned with that.
Do as Weed says and get the volt meter out. I don't think i would hook it into the cigar as there are lots of plug-in adapters that will use all the juice that that wire will provide for the lighter socket. If the guage pulls less than 5 amps then yeah go for it, but it's most likely a 10amp fuse???

If you want to keep things off of the batery and tucked. If you go under the steering column you can find the ignition and accessory wires. Get a T-tap and grab your connection. Here's a list of all the wires:
12volts red (x2) + ignition harness
Starter yellow + ignition harness
Second Starter N/A
Ignition pink/white + ignition harness
Second Ignition pink/lt. green + ignition harness
Third Ignition pink/yellow (10 awg) (3rd acc) + ignition harness
Notes: This wire is not required for remote start. It only provides power to the power window circuit.
Accessory dk. blue & pink/yel (16 awg) + ignition harness
Second Accessory pink/yellow (14 awg) + ignition harness
Keysense purple/tan - ignition harness


I would use the Pink/yellow 3rd ign wire to power up your tach.
Also, if you hate the ding ding when your key is in the ignition you can cut the keysense wire.

 

yes sir

 

and just in case someone doesn't know how to check for the right slot, half way (2:00) through this video, the guy is demonstrating how to find something hot in the fuse box. This is just a FYI for anyone too nervous to go poking through their fuse box. It won't bite!



http://www.youtube.com/watch?v=-CZ3aH4DBVc

 

Thanks guys. Did not think this would be more than a two minute install. Between the tight fit on the inline fuse and not finding the right power source, it has been maddening. I'll poke around some more in the fuse cluster and if all else fails go to the iginition wiring as DirtyDog mentioned. I don't think cig lighter will work as it is hot all the time.

 

Ok, I figured it out and got my gauge working fine. So I'm posting my findings in case someone else down the road is in a similar situation. The row of fuses 10, 25s etc. are all "hot" including the "spares". If you look at your inner cover, it also lists a "block" of outlets that are "relays". These numbers are like #68, #69. As soon as I saw "relay" I figured this is where true "accessory" juice (key must be on) and it worked. I used #69 (a spare) and tapped into it with a 10 amp fuse and everything works fine w/ ignition on and nothing when off...perfect! JoeHemi's video shows the same connection area.

 

I was just gonna say use the #69 relay. I tapped the trigger for the relay on my lights to there so they lights only power up when the ignition is on.