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Discussion Starter #1 (Edited)
I helped my brother install a remote starter on his wife's 2002 Dodge Caravan this week, and while this isn't Patriot specific, it's still good information as far as the wiring goes (having to deal with the Chrysler BCM/TIPM and what not). For wiring diagrams and help on this, www.the12volt.com had invaluable information on it.

There are very few high current wires under the dash these day and with the Body Control Module controlling most things, very few wires too. A lot of the switches use a multiplex signal wire, meaning one wire will carry the signal for various switch positions. They do this using a ground wire to a low voltage (5 volts or less) source in the BCM, and change the voltage through resistors. For example, the ignition switch only has five, 18 ga wires (Ground, Multiplex ground return, starter engage, +12 volt switched and +12 volt constant) to it and one of the wires sends a different voltage depending on the switch position. I observed the following voltages:

Key off and out = 4.55 volts
Accessory position = 3.5 volts
1st run position = 2.4 volts
Run position = 1.1 volts
Start position = 0.65-0.45 volts

So what does this mean? Well in order to remote start the vehicle, and have the heater get power we had three splices to do. First we interrupt the start wire (the remote starter has a key side and harness side hookup so you can install a dead switch if wanted, otherwise it's a pass through) and splice into the +12 volt switched. This get's the vehicle partially turned on and the starter cranking, but it won't run. The last step is to splice into the multiplex wire then use a fixed resistance to ground on it. Thanks to the above mentioned website, we found out we needed 180 ohms of resistance. So off to radio shack I went. They didn't have a single 180, so I bought a 150 and 33 ohm pack (they sell them in packs of 5 for .99 cents), then ohmed them to find the lowest ones out of each pack. Putting the two in series gave me 181 ohms. So we spliced into the wire, and as a test I held the wire to ground when my brother hit the remote starter button. It ran! But wait...the heater/ac blower wasn't getting power. So I let go of the wire to see if it was turned off. When I did, the heater turned on. Aha! So, this only needed to be grounded while the starter was turning, so a quick relay wired into the starter circuit and we had it working.

The next step was to have the park lights flash and turn on when running (to have a visual indicator when looking out the window). Again we had to deal with a multiplex signal from the headlight switch. The info we had said 2.1k ohms was needed to turn on the park lights and 790 ohm to turn on park lights and headlights. So essentially the lower the resistance, the more lights we turn on. It didn't work. When I put a 2.1K ohm ground to the wire, all the lights came on. So on a whim, I found a 3.3K ohm resistor and put that in place of the 2.1k one and was again greeted with success. Only the park lights turned on.

So what does this all mean for our Patriots? Well if you are thinking of hooking up to any under dash wires or switches have a digital volt meter (DVOM) handy and be ready to read voltage and resistance (which may mean disconnecting the battery while you do your resistance tests). It also means these are ground triggers, not voltage and accidentally pushing 12 volts into that wire my blow something in the BCM/TIPM. I found that by back probing the wires for voltage, I always found one that would change voltage from various switch positions. Then I would disconnect the battery and read resistance changes on that same wire. Once you find the resistance value, you can then tap that wire, run through a relay to ground with a resistor or two in series and activate that same function (and if for some reason it's not working as expected, try raising or lowering the resistance value until it does).

I figured this might be useful for any one thinking of playing with adding led's for the rear clutch or whatever. Isolating what you are doing with a relay is a good idea (so as not to add additional resistance and possibly change the function). Also, if things are acting strange after your hookup, you may need to add a diode into your hookup so that you don't accidentally add more resistance all the time. Check the12volt.com for help and look at other years diagrams too. The 2002 Caravan diagram did not mention the 180 ohm thing for the starter, but the 2001 and 2003 ones did.
 
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