bcm vs ignition harness
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=128800
Printed Date: May 15, 2024 at 1:15 AM
Topic: bcm vs ignition harness
Posted By: c.c.autospa305
Subject: bcm vs ignition harness
Date Posted: October 10, 2011 at 6:59 PM
I'm wondering is it possible on some vehicles for the there to be an additional wire that test positive for ignition and starter circuits at the body control module(bcm)? I recently installed an alarm on a 2005 Pontiac Grand Prix and I noticed it previously had an alarm installed because the last installer left all his t-taps on the corresponding wires necessary for an alarm connection. I don't remember the wire colors but I tested and confirmed ignition AND starter wires at the bcm. I looked at the ignition harness only to see those wires untouched which made the job look a little cleaner. Can anyone add any insight into this, please.
Replies:
Posted By: Twelvoltz
Date Posted: October 10, 2011 at 7:42 PM
Yes it is very possible that the wires run right from/to the BCM from the ignition switch. That 05 Grand Prix is one that it's easier to catch the wires on the left of the column/dash/at the BCM than at the ignition switch. The problem is, that just because a wire at the BCM behaves as ignition it does not mean it is the correct ignition wire. On some vehicles, if you try to power ignition/accessory/etc wires at the BCM you could cause damage to the vehicle. Safest way is to go to the ignition switch.
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Installer, IT support, and FFL. I need less hobbies.
Posted By: c.c.autospa305
Date Posted: October 10, 2011 at 8:44 PM
Okay, thanks for the reply and info. Most basic alarms won't send power to the ignition/starter wires, just used as an immobilizer, correct? That would only apply when installing a remote start?
Posted By: howie ll
Date Posted: October 11, 2011 at 2:55 AM
Just a silly thought re: the first post; T-taps and installer don't go together too well. 
On a more professional level that rule doesn't apply to all cars, it's also simply a point of convenience. ------------- 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.
Posted By: c.c.autospa305
Date Posted: October 11, 2011 at 3:34 PM
What's the professional, industry standard way of making wire connections Howie? Solder?
Posted By: howie ll
Date Posted: October 11, 2011 at 3:40 PM
Of course with NO. with no exceptions. See the posts in the general discussion section.
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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.
Posted By: howie ll
Date Posted: October 11, 2011 at 3:44 PM
Sorry about the typo, doing it on my phone whilst watching TV! Not clever. In brief, yes with no exceptions.
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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.
Posted By: c.c.autospa305
Date Posted: October 12, 2011 at 11:07 AM
What kind of solder(size & type) is typical for electrical conncetions in wiring an alarm, remote start, remote windows, etc.?
Posted By: c.c.autospa305
Date Posted: October 12, 2011 at 11:08 AM
typo....connections*.....sorry
Posted By: buddholly
Date Posted: October 12, 2011 at 3:38 PM
I use a military splice on all wires except data connections and underhood connections. Saves a ton of time on soldering and eliminates any "bad" soldering. Plus it can be a PITA when trying to reach wires and are trying to solder in a small space.
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Posted By: c.c.autospa305
Date Posted: October 14, 2011 at 5:56 AM
What is a "military splice?" Let me go try googling that and see what I come up with.
Posted By: howie ll
Date Posted: October 14, 2011 at 7:10 AM
To save us repeating ourselves, look in the section here on General Discussion. On the first page are two very long and informative threads on soldering and connecting.
This thread is rapidly turning into 101 on auto-electrics, I've neither the time nor inclination for such basics and reading those threads will help you to understand.
Just about every query ref: car electrics has come up before, just look in the archives.
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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.
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