Printer Friendly Forum Posts - Door trigger, 2005 Ford F-150

Hello all I'm having trouble with when I have the viper 5706v armed and I try to remote start the truck the alarm goes off saying that a door was open I have a 2005 ford f150 no extended cab just 2 seats it came with a remote to unlock the door no combo panel on door I connected the door trigger wire for alarm at the bcm

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Matt

Typically this happens when the BCM sends a negative pulse to the doors. You will need to wire +12v thru a 10k resistor to the alarm (-)trigger wire after the diodes to bias the alarm (-) trigger so negative pluses can't deliver ground to set off the alarm, only a constant or longer negative trigger will drain the (+)bias to ground.

The only other way is to diode isolate the BCM from the vehicle door triggers which also stops the RAP shutdown and the dome light from working.

I don't quite understand what your explaining are you saying after the two diaods I already have installed I need to undo after the diaod add a 1k resistor and apply 12vdc constant to the resistor sending it into to negative door trigger wire going to the viper system is that correct. If so won't that create a direct short at the resistor

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Matt

You attach (ADD) the +12v 10k resistor to the end of the 2 diodes that are already attached to the alarm wire (-) door trigger. The resistance is to high to create a short. you are only adding a small amount (trickle of current) at 12v which dissipates when direct grounded by door trigger. Basically offsetting the negative pulse from the BCM that would trigger the alarm. The +12v is stopped by the diodes never making it to the vehicle side.

OK I understand what your saying now ok and will that deplete the battery my truck sometimes sits in the grage for a few days with out starting

And also you had said 10k on the last post and you said 1k what one did you mean

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Matt

Typo missed the zero and corrected it. no will not deplete you battery not enough current to even light up a 2v led

Alright awesome I will give that a shot and keep you posted with the results

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Matt

ok i tried out the solution and it did not work it compleatley disabled the door sienceing on the alarm when i opened a door it did not even know i did

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Matt

Are you sure you got a 10k=10,000ohms resistor? Would check and make sure it is the right resistance. Let me know how you wired it. Should have only had to add the resistor to the wire/diode connection with out disconnecting the diodes you already had hooked up.

OK I tried to upload exactly what I wired up into the truck

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Matt

Sorry messed up the pictures

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Matt

Resistor needs to be between the red wire and the diodes in your pic.The yellow wire needs to be hooked to the diodes. The resistor is supposed to limit the 12v input from the red wire into the existing wiring. As you have it wired now you are putting full 12 into vehicle so you can't get to zero ie ground! posted_image

ok that did not work either the doors are negative trigger the viper system does not detect the doors again with the way the diaods are placed the only way the door are detected placing the diaod block lines toward the truck wire not toward the the green viper wire

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Matt

Have a question if by ohms law e=I.r 10.10000=.001vdc. If I were to turn the diode block trwrd the viper system and the voltage being in the hundreds of a single volt would that hurt the BCM

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Matt

Been awhile since doing a Ford alarm install. Looked it up and Yup your right diodes are backwards, everything else should be right.

OK so to be sure were on the same page I need to turn the diodes around and let that hundredth of a volt go into the BCM I am trying to avoid buying a new BCM if you know what I mean

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Matt

mmatrisch wrote:

Have a question if by ohms law e=I.r 10.10000=.001vdc. If I were to turn the diode block trwrd the viper system and the voltage being in the hundreds of a single volt would that hurt the BCM

That's why such a high resistor on the (+)12v so the amperage is minimal as to not damage anything. It's amperage that is the killer in 12v systems. posted_image

This is the traditional way but the second set of diodes cause the doom light and RAP shutdown to stop working. Deleting the second set of inline Diodes between BCM and door triggers and adding the !@v with resistor elininates this problem.

Ok that's what I was thinking too but I just wanted the second ok I work with AC voltage bit not DC ok I'm working at the moment I'll keep you posted

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Matt

No problem, keep me updated.

I was thinking about that exact pictorial somatic to block the excess back voltage I'm glad you pointed out the RAP problem that it creates I have a question where o you get the picture diagrams like you had just posted is that something I can buy and add to my collection of stuff

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Matt

Either by searching the forums on this site or varied key word google image searches. No direct source as of yet just a lot of work and from memory. Sometimes my memory gets a little fuzzy and have to refresh it. Would be nice if there was a searchable repository like that to search from.

Since I know nothing about F Series might I ask if the door switches are open circuit when the door is opened?
How's about wiring to the domelight and disabling the door ajar warning.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

No they are not open circuit they are 0v (ground) when opened. the problem with the dome light is the 30 second off delay. Most people don't want to wait for the light to go off so they can arm the alarm. So it doesn't give the second bypass chirp. I have heard of wiring a relay in to disconnect the negative trigger input wire while the dome light is on using the ground when armed. The BCM controls the door ajar, dome light, and RAP shutdown from the door triggers. The driver door and all other doors are indicated ajar separately.

OK turning the pair of diodes around worked now the alarm does not go off when I try to remote start the truck I wired the constant 12vdc on after the fuse for the viper system in case I get a direct ground short it does not blow a fuse in the truck that has something to do with safety or functionality. Do you think I should draw out a scmatic of the finished product so someone else can use the help

Again thanks for all the help guys matt

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Matt

All +12v feeds should have a fuse even if it is shared between multiple low draw relay coils and the like.

Sure that what this site is about I help you you help someone else, basically pay it forward.

lurch228 wrote:

Typically this happens when the BCM sends a negative pulse to the doors. You will need to wire +12v thru a 10k resistor to the alarm (-)trigger wire after the diodes to bias the alarm (-) trigger so negative pluses can't deliver ground to set off the alarm, only a constant or longer negative trigger will drain the (+)bias to ground.

The only other way is to diode isolate the BCM from the vehicle door triggers which also stops the RAP shutdown and the dome light from working.

@lurch228 I recently did a 2004 Chevy Tahoe with a similar predicament. I installed used a Prestige 997E with an Flashlogic bypass and during a remote start, the alarm would go off. Tech support said other installers had run into a similar issue and the cause was at the BCM.

Would this have fixed it? I confirmed via the key fob that it wasn't the trunk or hood pin being triggered. I ended up setting the 997E to Unlock before & Lock after start to bypass the issue.

Yes on the Ford f150 the bcm sent out a negative pulse to make sure the dome light is not on and the alarm system thinks the door was open so placing the resistor in the circuit as shown above creates a filter for the quick check that the bcm does it also have a very small delay when the door is actually open but it is almost negligible because the the actual ground conductivity between the two is much larger when the the door is open to when the bcm sends out its pulse

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Matt

These are 2 different issues. This is a Ford BCM design function checking issue, From what I know yours is a factory alarm (security function) needs to be disarmed to remote start by unlocking. I haven't and don't know of anyone who has tried to do this on a Tahoe to see if it would work or not. With the Ford it's setting off the aftermarket alarm, not the OE alarm.

lurch228 wrote:

These are 2 different issues. This is a Ford BCM design function checking issue, From what I know yours is a factory alarm (security function) needs to be disarmed to remote start by unlocking. I haven't and don't know of anyone who has tried to do this on a Tahoe to see if it would work or not. With the Ford it's setting off the aftermarket alarm, not the OE alarm.

Good point. Thanks for the explanation!