many devices of one 12v Constant
Printed From: the12volt.com
Forum Name: Car Security and Convenience
Forum Discription: Car Alarms, Keyless Entries, Remote Starters, Immobilizer Bypasses, Sensors, Door Locks, Window Modules, Heated Mirrors, Heated Seats, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=77845
Printed Date: May 10, 2025 at 2:19 AM
Topic: many devices of one 12v Constant
Posted By: bigman17
Subject: many devices of one 12v Constant
Date Posted: May 15, 2006 at 11:57 PM
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?
Replies:
Posted By: Twelvoltz
Date Posted: May 16, 2006 at 7:55 AM
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.
Posted By: bigman17
Date Posted: May 16, 2006 at 8:03 AM
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
Posted By: dxdenis02
Date Posted: May 16, 2006 at 11:53 AM
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
Posted By: bigman17
Date Posted: May 16, 2006 at 2:05 PM
1) Is there any way to determine current without cutting the wire? 2) Given that there is enough power in the 12v Constant to power everything, what size fuse should I tap the 12v constant, remember about 5 relays will be operating from that one fuse.
Posted By: dxdenis02
Date Posted: May 16, 2006 at 2:13 PM
1 no are you using the 12v to drive the relays or the relays and then relay are powering something else like what you listed if its what you listed i would start with a 30A since these are not going to be constant draws just momentary
Posted By: bigman17
Date Posted: May 16, 2006 at 2:24 PM
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.
Posted By: Twelvoltz
Date Posted: May 16, 2006 at 8:37 PM
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.
Posted By: bigman17
Date Posted: May 16, 2006 at 9:36 PM
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? Thank you very much!
Posted By: Twelvoltz
Date Posted: May 17, 2006 at 8:00 AM
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.
Posted By: bigman17
Date Posted: May 17, 2006 at 1:27 PM
Thank you very much for explaining all that, it helped tremendously! I just have a coulpe more quesitons: 1) I made a mistake the tilt sensor does have a 1 amp fuse on it, is it alright to still tap into the brains power after the brains fuse? 2) I am going to need one more relay for the GM VATS bypass, where should I get the 12v fused for this one? 3) Although I can get power to my accesories by using the alarms fuses Im still going to have to make 3 direct connections to the 12v constants in the ignition harness. The diagrams for my car didnt show it but I found 2 12v constants. Here are the wires that need to be connected, my question is what size fuses should I use for these for these connections: A) Brains power B) XRC first 12v power input C) XRC second 12v power input A and B I plan to connect the first 12v in my ignition harness and C I plan to connect the second 12v in my ignition harness. Thanks again.
Posted By: Twelvoltz
Date Posted: May 17, 2006 at 2:48 PM
1. Since it has it's own fuse put it inline, but before the fuse to the brain.
2. You can power this relay from the XCR as well, after the fuse to the brain.
3. Do not change the value of the 30amp fuses that are currently inline, they are sufficient to power what you need.
Make sure the wire you are connecting the 3rd connection to is strong enough to handle the load you will be putting on it. Make sure that it is indeed a constant hot that is of ample gauge and supplies the ignition switch, not another device.
Hope this helps
Posted By: bigman17
Date Posted: May 17, 2006 at 2:56 PM
The instructions say those fuses are just to protect the unit it self and every time a 12v from the car is taped to fuse it accordingly. The second 12v constant i found was tied with the other ignition wires and is the same guage and is indeed a constant but I do not know what it does. Would is be safer just not to connect that second 12v input on the XRC? Thanks
Posted By: Twelvoltz
Date Posted: May 17, 2006 at 3:20 PM
bigman17 wrote:
The instructions say those fuses are just to protect the unit it self and every time a 12v from the car is taped to fuse it accordingly.
Understood, and if you really want to, you can provide a seperate fuse for each device you are adding, this is the absolute best way to do it! I am just explaining how I do it (as well as how I was tought to do it). If the device had a large current draw, or it's own fuse then I would definately not use the 30amp fuses that are included, however in your case you do not really have a need to add all of those fuse holders and extra fuses.
bigman17 wrote:
The second 12v constant i found was tied with the other ignition wires and is the same guage and is indeed a constant but I do not know what it does. Would is be safer just not to connect that second 12v input on the XRC? Thanks
If it is in the ignition harness, it is probably ok. However if you cannot verify it indeed supplies the ignition switch, I would not use it.
Posted By: bigman17
Date Posted: May 17, 2006 at 3:32 PM
Yeah im not sure what that second wire does so im just not going to use it. Do I need to connect that second 12v input from the XRC to something or is it optional? And just to be safe and because I have a lot of inline fuses i am going to fuse that A) Brains power and B) XRC first 12v power input , what size fuse should I use for each one or can I just connect both wires to one fuse(size?). Thanks a lot for your time. O and I was just curious why does the trunk release need a relay but the parkling lights do not?
Posted By: Twelvoltz
Date Posted: May 17, 2006 at 3:47 PM
You need the second input to the XCR, it is mandatory.
The Brain and XCR fuses are included in the system and do not need their value changed, what you are adding to these feeds will not exceed what they supply.
The relay for the parking lights in built into the unit.
Posted By: bigman17
Date Posted: May 17, 2006 at 3:58 PM
So just connect both 12v inputs on the XCR to the same 12v source? Twelvoltz wrote:
The Brain and XCR fuses are included in the system and do not need their value changed, what you are adding to these feeds will not exceed what they supply.
I mean the fuses i want to put within 12 inches of tapping the 12 volt source(for brain, 2 XCR wires) what size fuses should I use and can I connect all three to one fuse? Thanks
Posted By: bigman17
Date Posted: May 17, 2006 at 6:56 PM
I just looked at the manual and there is a THIRD 12v constant to the XCR? RED / white
Posted By: Twelvoltz
Date Posted: May 17, 2006 at 8:24 PM
The three large wires going to the XCR currently have fuses in them. If you want to be as safe as possible, move the fuseholders closer to where you are tapping into the ignition harness, or add additional fuses right at the ignition harness the same value as what is currently inline now. The older DEI pieces also had 3 supplies into the XCR, but the RED / white was jumpered to one of the reds at the XCR itself. Hook all to the constant hot of the vehicle.
Posted By: bigman17
Date Posted: May 17, 2006 at 8:30 PM
Alright thank you very much for your help Twelvoltz. Hopefully all goes smooth when I install it Saturday morning.
Posted By: bigman17
Date Posted: May 18, 2006 at 9:19 PM
I was connecting up the trunk release relay exactly like the manual said and when I activated it from the remote it blew a fuse. I tested the wire in the factory release switch and it goes from -0.01v at rest to +0.02 when pressed. Did i do something wrong?
Posted By: Twelvoltz
Date Posted: May 18, 2006 at 9:37 PM
Trunk release using channel 2 output from 791XV
Pin 85 Constant fused +12V
Pin 86 RED / White channel 2 output from 791XV
Pin 30 Constant fused +12V
Pin 87 Output to LeSabre BLACK/ white positive trunk release
Posted By: bigman17
Date Posted: May 18, 2006 at 9:52 PM
ok ill try that. I used an ORANGE / black wire for positve trunk release but also this is how i wired it which i got from the manual: Pin 85 RED / White channel 2 output from 791XV
Pin 86 Constant fused +12V
Pin 30 Output to LeSabre positive trunk release
Pin 87 Constant fused +12V
Posted By: Twelvoltz
Date Posted: May 19, 2006 at 10:22 AM
All circuits must be verified with a DMM before hooking anything to them. If you are blowing the fuse, that leads me to believe that you are throwing +12V to ground, meaning you are on the wrong wire. Did you verify that this wire goes to +12V when engaging the trunk release in the vehicle?
The tech sheets are nice time savers, but you should ALWAYS verify the operation of a wire before tapping into it. You can cause some serious damage to the vehicle if you just connect wires without verifying their operation!
Posted By: bigman17
Date Posted: May 20, 2006 at 11:37 PM
k got the trunk release working perfectly. But now i have a problem, i was wiring up the parking light flash but when i tried it the lights did not flash and now the parking light switch does not work. I tested the wire i was using and it when from 0 at rest to 12v when pressed but when i tied the wire from the alarm to the wire behind the switch it broke the switch i guess. I removed the wire from the alarm but still the switch doesnt work but the actual lights do work. Do you have any idea what this could be?? Thanks
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