powering off ignition harness

In theory, when you have an ignition wiring harness with high current leads feeding constant power to the ignition switch, you should be able to use those leads to power your remote starter and the various ignition outputs(ignition, accessory and starter wires) needed to start the vehicle. Essentially, replicating the act of turning the key. My question is, how do you determine which 12+ constant feeds power which outputs in the ignition harness? Are there any tip or tricks to figure it out? Life is pretty simple when there are only one or two power feeds in the ignition harness, however, things get more complicated when there are three or four. For example, I've run into this situation with both a 2003 Jeep Liberty and a 2006 Dodge Dakota. The Dakota has three power feeds(40a each) going into the ignition switch that power two ignition wires, four accessory wires(3pos & 1neg) and one starter wire. As you can imagine, it would be very easy to misjudge how to distribute the power requirements among the outputs without overloading one of them. (BTW, in a situation like that, I'd just go to battery for my power needs rather than guess).

Best way would be to consult a wiring diagram for the vehicle. Dodge and GM run the Blower current through the IGN switch. Ford has a Blower power relay, so Ford doesn't run the Blower current through the IGN switch. The Blower load is roughly 10 amps max. And everything else combined is probably less than 10 amps. Plus the starter solenoid, which is intermittent. IMO it doesn't really matter which inputs go to which outputs. Even if you put all the load on one input circuit, I doubt it would exceed the 40 amp rating. It wouldn't surprise me if total load is less than 20 Amps, including the blower. In a Dodge, figure out which output is the Blower, put an RS ACCY circuit to it, with that RS input to one of the feeds, and power everything else from another feed. It would be fine.

davep. wrote: Best way would be to consult a wiring diagram for the vehicle. Dodge and GM run the Blower current through the IGN switch. Ford has a Blower power relay, so Ford doesn't run the Blower current through the IGN switch. The Blower load is roughly 10 amps max. And everything else combined is probably less than 10 amps. Plus the starter solenoid, which is intermittent. IMO it doesn't really matter which inputs go to which outputs. Even if you put all the load on one input circuit, I doubt it would exceed the 40 amp rating. It wouldn't surprise me if total load is less than 20 Amps, including the blower. In a Dodge, figure out which output is the Blower, put an RS ACCY circuit to it, with that RS input to one of the feeds, and power everything else from another feed. It would be fine.

Interesting. I'm surprised the loads are that low. I guess manufactures are over engineering their electrical circuits to CYA. That probably explains why some RS manufactures, such as some of the older Design Tech DIY products, power everything off a single 10ga feed fused @ 30A.

OOOOPs! Heated Seats go through the Ignition switch. the source I use for wiring diagrams doesn't have 2006. So I used 2004. I just looked at 2005, and there are subtle differences. BUT it shows Heated Seats powered through the IGN switch with no relays. So I was wrong. With the seat heaters on, the load will very likely exceed 20 amps. But could still be less than 40.

I've always assumed there wasn't much rhyme or reason for the way wiring diagrams were laid out, but is there? What I mean is this...Look at the wiring diagram for 2005-2007 Jeep Liberty. There are two accessory wires, both pink / YELLOW. One is labeled Accessory 1 and the other Accessory 2. Now if you look at the wiring diagram for 2006 Dodge Dakota, you'll see Accessory 1 is listed as a (-)purple and (+)pink/white, and Accessory 2 is listed as 2 pink / YELLOW wires. Are they suggesting that with the Liberty you isolate each accessory wire due to the load placed on it? Whereas with the Dakota you can group both wires listed for Accessory 1 and then group both wires listed for Accessory 2. (Granted you'd have to use a relay to reverse the polarity for the (-)purple in Accessory 1). Maybe I'm just over tired and over thinking it. lol

The "Wiring Guides" are helpful, but leave a lot to be desired when trying to figure out exactly what is really happening. Again, having the diagrams for the vehicle answers a bunch of questions. Looking at how the IGN switch is wired, and to what, helps immensely with figuring out how to wire the RS outputs. I looked at the 2006 Liberty. They indeed show two yel/red wires, but they are not the same. One is hot in RUN ONLY, but not START or ACCY. This wire powers pretty much everything that is switched with the IGN. Heated Seats, HVAC, power mirrors, AirBags, tire sensors. The other yel/red is hot in RUN AND ACCY, but not START. It powers the wipers, radio, and is an input to the BCM. So test the two yel/red wires. The one you want to power as an ACCY (not powered in START) will test as B+ in RUN only. The other one (wipers and radio) can probably be ignored, but will test B+ in ACCY as well as RUN. I don't like the wipers powered during a RS (if its easy to isolate), because damage can occur if there's heavy snow or ice, or the glass is dry, and the wiper switch was left on the last time the car was driven. In this case, the radio won't work either during a RS, but this may not be a problem in an unoccupied car, and the radio won't remain on after a timed-shutdown either waiting for the RAB to time-out and shut the radio off. Testing and Diagrams. And thinking it through.

Hi,     Looking at your quote "IMO it doesn't really matter which inputs go to which outputs. Even if you put all the load on one input circuit, I doubt it would exceed the 40 amp rating. It wouldn't surprise me if total load is less than 20 Amps, including the blower." An issue that can happen if battery power is obtained from a lower current source, say a 20 amp circuit. The customer operates remote start, gets in vehicle and operates accessories before doing a take over. The lower current supply, now trying to supply accessories it wasn't intended to power, overloads and blows the fuse. This could result in a service call, or a tow-in. And yes I've seen it.     As for determining which feed wire supplies which switch output, determine feed wires/terminals, disconnect switch and use an ohmmeter. Mark

Ween wrote:     As for determining which feed wire supplies which switch output, determine feed wires/terminals, disconnect switch and use an ohmmeter. Mark

Simple, and brilliant! Very helpful Ween, thanks!

Ween wrote:     As for determining which feed wire supplies which switch output, determine feed wires/terminals, disconnect switch and use an ohmmeter. Mark

Ah, that makes sense. So simple. Kinda makes feel stupid for not thinking of that. Thanks!

davep. wrote: I don't like the wipers powered during a RS (if its easy to isolate), because damage can occur if there's heavy snow or ice, or the glass is dry, and the wiper switch was left on the last time the car was driven.

That annoys me. I guess I never thought to try and isolate them when remote started. Seems like it might be easy enough to interrupt the power supply to the wiper motor with a relay when remote stated.