many devices of one 12v Constant

Since I am going to have many relays and other such things hooked in my alarm can I tap the 12v constant from the ignition harness once and fuse it then connect all the relays to the end of that fuse? Also i think there is also second 12v constant in the ignition harness that was not listed in the wiring diagrams , is there a way I can meaure the current of the wire with my multimeter?

It really depends on what you are driving with these relays. Listing the vehicle make/model/year, system model, and what you want to install would help. If you are driving just parking lights, and a trunk release then the constant in the ignition harness would be fine. If you are planning on running driving lights or other high demand pieces then you should run the relay supply wire direct to the battery with a fuse at the battery. Hope this helps.

96 Buick LeSabre and Viper791 xv.  I need the power for things like tilt sensor power, relay for unlock, trunk release, horn honk, maybe 1 or 2 other low current devices.  Can I just use one fuse? and if so what size fuse. THanks

you can def measure current with your meter if it has that option. if it does the meter will list it max current handling. now to measure current you need to break the line and but the meter leads between it. for example i have a fluke here st work that i take home on the weekends for alarm installs. i have a setting with A with a straight line and another a with a sine wave (dc and ac)  and the meter can handle 300mA and in the 2nd position 10A. look for aomething similar and put you leads between the cut lines and measure away   good luck  ps a typical ign wire should handle 40A more then enough for low draw relay triggering and additional alarm sensors

  I'm just using it as the 12v fused constant for relays controling switches for parking lights, truck release, locks, horn and to power the tilt sensor.

bigman17 wrote: I'm just using it as the 12v fused constant for relays controling switches for parking lights, truck release, locks, horn and to power the tilt sensor.

OK.... Parking lights; the system has a built in relay for this Trunk release; this is only active for a very short period of time, I usually power this relay from one of the large wires powering the DEI XCR pack on the brain side of the fuse. Locks; your system has the outputs built in that can handle triggering the factory relays Horn; your system has siren positive output, this can be programmed to be a pulsed output to trigger a horn, but would not work properly for a siren if changed. If you are going to do horn honk then you will need a relay for this, but the draw on this wire would be minimal as you are sending ground to honk the horn. You can hook this relay's supply to the brain side of the fuse of the XCR pack as well. Tilt Sensor; if this has a fuse inline already, just connect it to one of the heavy wires powering the XCR pack just like your trunk release relay. If it does not, add a fuse holder inline (a 5amp fuse is probably sufficient here), but still connect it to the same heavy wire that powers the XCR pack. So...you only need one additional relay that you can power off your harness for the 791XV (2 if you decide to not use the siren, but the horn instead). No need for an additional fuse holder. Hope this helps. Keep us posted.

bigman17 wrote: 1) Whats an XRC pack? 2) the parking light diagram in the manual for the 791xv shows the (-) output to be 200mA (so I dont think its relayed) 3) The only reason i need a relay for the unlock is for the first unlock pulse to power the unlock motor, the 2nd unlock pulse will go right to the switch in the door with out a relay. 4) THere is a seperate brown (-) 200mA Horn wire on the alarm. How should I connect this. 5) The tilt sensor does not have have a fuse but can I just tap the power line of the shock sensor connector?

1. The XCR is what DEI refers to as the extreme capacity relay satellite pack. This is the box with a ribbon cable running to it from the brain that has the heavy gauge constant hots, ignitions, starter, and accessory wires coming from it. 2. If you are using the positive output then there is no relay required. If you are switching the polarity output of the jumper to negative it only supplies 200ma. Your vehicle has a positive wire for parking lights, so leave the jumper as is and just connect to the parking light positive trigger. 3. You are correct, you would need an additional relay to do driver's door priority unlocking. This relay can be supplied by either of the reds or the RED / white supplying the xcr pack. 4. My apologies, you are correct, the h4 brown is indeed a horn honk output. However you may not need a relay to drive the factory horn. What I do to determine if a relay is needed is to verify the operation of the wire with my DMM. Once I have established the wire is indeed the wire I am looking for (in this case the horn wire), and that it is switching negative to activate, I will take out my old Matco standard bulb test light. Put it to ground, and tap it to the device's negative trigger wire, if the device functions, then I will just hook system's wire directly to it. If the device does not operate then I will add a relay. 5. The shock sensor power wire is a very low current supply, although it may work fine, I would say to tap this wire into the red constant input to the brain of the alarm. This fuse is smaller than the ones on the XCR, and will provide adequate protection without the need for an additional fuse holder. The only device you are adding that will draw a significant amount of current is the extra relay for driver's door priority unlocking. But this is only active for .8 seconds, and will not draw excessively from the constant supply of to the xcr pack. Also, to make sure I am clear, all connections I am recommending to tap in are to be made between the fuse and the brain of the system...you are using the DEI supplied fuses to protect the devices/options you are adding. Hope this helps.