Need IGN / d+ signal - splice off alternator?

I'm installing a DC-DC charger for my house battery. I need a d+ signal, which is essentially the IGN signal from the alternator (telling the charger that the engine is running so it doesn't just drain the starter battery). Can I just tap into the wire coming off the alternator that powers the IGN light? Finding the thing coming out of the fuse box based on color in a huge wire bundle seems like a needless nightmare.

 

If it just needs to be a switched 12v, I would look at the fuse box in the engine bay for a switched circuit and use an add-a-circuit to pull power from that. It'll be easier and less intrusive than using a wiretap in a hard-to-reach area.

 

Thanks, this is perfect, I didn't know this thing existed.

There are however two fuses labeled "IGN" in the cab fuse box - how can I figure out what they are? Is there a guide somewhere to the exact meaning of all the fuses?

 

I've found the easiest way is a multimeter. They're inexpensive and really easy to use and very handy when doing electrical work. You would just get a multimeter and start checking fuses to see if they're 0v when the truck is off and 12v when the truck is on. You don't even need to remove them, the fuses have little metal bits on top you can touch the multimeter to.

Or do some digging around here and see if anyone has identified a switched 12v under the hood. Or if in-cab fuse is fine, there should be one called ACC for accessory that will work, but I figured you'd be mounting the DC-DC controller under the hood.

 

You should be able to search around and fine the fuse most folks tap for this purpose, I dont recall off the top of my head. I know 3rd gen electronics are more sensitive than previous generations and some folks have reported issues when tapping the wrong fuse.

 

The in-cab fuse will be fine if I find the right one. I don't think ACC is it, this is a specific signal that comes straight from the alternator.

The charger will go in the bed with the rest of the house power setup, I'm running the power with 4 ga welding cable under the chassis and will run this signal wire along with it. Either way I'd have the same cable run.

 

If it's a specific signal that it needs then I'm not too sure if the add-a-circuit will suffice, I thought it only needed generic switched power to tell the charger if the truck was on or not.

 

Yep, that's my worry. Hopefully someone finds this thread who has done it. I have found a couple of threads where people say "I tapped off the IGN fuse in the cab" to do something similar, without saying which fuse they mean (two of them have IGN in the name). I'm off to see if Youtube has an answer.

 

A quick glance at this article and it seems like any switched 12v off of the fuse block will work.

https://renogy.force.com/helpcenter/s/article/How-To-wire-D-signal

 

SOLUTION (I think) someone on Youtube tapped the 10 amp ACC fuse in the engine bay fuse block -- so thank you person who said ACC wire, and also who suggested the add-a-circuit which this guy also used. He's installing a similar device that needs the same signal. Link for posterity:
https://www.youtube.com/watch?v=SVAedNREYRk

 

Thank you, this is it.