car with multiple 12 constant wire

on cars that have multiple how do you deceide on what wire to use for remote start applications, my 03 taurus has 4 of these wires but the alarm only has 2 outputs. should i use a relay for the other two?

If you are asking about the wires at the Ignition Switch On your Taurus:

Usually those wires terminate together in the loom, Junction Box / Fuse Box or elswhere

You just need to be concerned if the wires in question will carry the added load of your RS....................which they will.

On some Vehicles U have to use a Constant from the Battery because the Switch wires or Fuse Block does not carry sufficient Power

MO

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Additional note to the above post. If you are putting in an alarm or starter. The constant wire that you should be concern about is the GREEN/ purle wire at the ignition harness. It's the one that can carry the load when you are putting in an alarm and starter.   Below is the wiring diagram for your vechile. DIRECTWIRE™ WIRING INFORMATION - FORD / TAURUS / 2003 / Remote Start 12volts lt. GREEN/ purple   +   ignition harness Starter RED / lt. blue   +   ignition harness Second Starter N/A        Ignition RED / lt. green   +   ignition harness Second Ignition N/A        Third Ignition N/A        Accessory gray / YELLOW   +   ignition harness Second Accessory BLACK/ lt. green   +   ignition harness Keysense           Power Lock pink / YELLOW   -   26 pin plug @ GEM Notes: The GEM (Generic Electronic Module) is to the left of the steering column. Power Unlock pink/lt. green   -   26 pin plug @ GEM Notes: The GEM (Generic Electronic Module) is to the left of the steering column. Lock Motor pink/black   5wi top plug of fuse box Unlock Motor RED / white   5wi top plug of fuse box Parking Lights+ brown   +   headlight switch or fusebox Parking Lights- N/A        Hazards           Turn Signal(L)           Turn Signal(R)           Reverse Light BLACK/ pink   +      Door Trigger BLACK/ orange   -   20 pin plug at GEM Notes: This wire controls the door ajar indicator on the dash, must cut the wire and diode isolate it from the instrument cluster. Can also use individual negative door trigger wires in the 26 pin plug at the GEM. They are: yellow/black (LF), gray/red (RF), lt. GREEN/ YELLOW (LR), and pink/lt. blue (RR). The GEM (Generic Electronic Module) is to the left of the steering column. Dome Supervision BLACK/ lt. blue   +   top plug of fuse box Trunk/Hatch Pin           Notes: On the sedans use BLACK/ pink (-) at the light in the trunk. On the wagons use WHITE/ purple (-) in the 26 pin plug at the GEM. Hood Pin tan/lt. green   -   26 pin plug at GEM Notes: The GEM (Generic Electronic Module) is to the left of the steering column. Trunk/Hatch Release           Notes: With keyless entry it is purple / YELLOW (-) at the switch. Without keyless entry it is gray/red (+) at the switch. On the wagon, to unlock just the rear hatch use yellow/lt. green (-) in the 26 pin plug at the GEM. Power Sliding Door N/A        Factory Alarm Arm           Factory Alarm Disarm pink/white   -   26 pin plug at GEM Notes: The GEM (Generic Electronic Module) is to the left of the steering column. Disarm No Unlock see factory alarm disarm        Tachometer tan / YELLOW   ac   PCM Notes: The PCM (Powertrain Control Module) is on the passenger side firewall under the hood. Wait to start N/A        Brake Wire RED / lt. green   +   brake pedal switch Parking Brake           Horn Trigger purple or blue   -   steering column Memory Seat 1           Memory Seat 2           Memory Seat 3           Immobilizer Bypass Module: Required: Yes Type: SecuriLock Part #: 556S, 556U, or 555U Notes: N/A        This wiring information is being provided free of charge on an "as is" basis, without any representation or warranty. It is your responsibility to verify any circuit before interfacing with it using a digital multimeter. Directed electronics, Inc. assumes no responsibility with regards to the accuracy or currency of this information. Proper installation in every case is and remains the responsibility of the installer. DEI assumes no liability or responsibility resulting from improper installation, even in reliance upon this information. Be careful whose advice you buy, but be patient with those who supply it.