constant 12v drops to 1.6v

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=92922
Printed Date: July 13, 2025 at 1:27 PM

Topic: constant 12v drops to 1.6v

Posted By: Toru
Subject: constant 12v drops to 1.6v
Date Posted: April 14, 2007 at 12:51 AM

Vehicle: 2000 Ford F150 (no factory keyless)
Alarm: Pyle 201

I am connecting a Pyle 201 primarily to get keyless entry. I have connected the +12 input wire on the harness to the GREEN/ Purple wire in the ignition harness (chart show that or yellow is constant 12V). The problem I have is as soon as the brain unit is connected to the harness the 12V drops to 1.6V. The alarm does not respond to remotes or the valet switch and does not flash its LED or chirp its siren.

Does anyone recognize this problem? Is the brain just DOA?

Replies:

Posted By: KarTuneMan
Date Posted: April 14, 2007 at 9:35 AM

How long does it take for this " low voltage" problem to happen? this trucks BCM shuts down after 5 or 10 min. after you lock the doors. For anything to respond, you need to "wake up" the BCM. If your alarm has a "factory alarm disarm" wire, pulse the keysence wire. This output triggers BEFORE the unlock pulse. It will wake up the BCM, so the unlock works.

Try it?

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Posted By: Toru
Date Posted: April 14, 2007 at 12:49 PM

I don't think it is BCM related. The voltage drop occurs as soon as the brain is connected and pops back up as soon as it it disconnected (pulling the fuse on the harness).

I've hooked the brain up to a 12V PS on the bench and it works fine. I've hooked the brain directly to the battery and it works fine. None of the "constant 12v" connections I've tried on the factory wiring harness work - they just drop to 1.6V.

I really didn't want to run a line out to the battery but it looks like that is what I'll have to do.

Posted By: mikvot
Date Posted: April 14, 2007 at 12:58 PM

That GREEN/ violet should definately not be dropping voltage like that. Make sure you have the right wire. I get it on the left side of the steering column, under the grey plastic ignition harness cover. Check all of your other wiring also.

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Posted By: Toru
Date Posted: April 14, 2007 at 11:47 PM

Problem solved: bad ground.

I was using a ground point that worked fine for a pair of relays but was not good enough for the brain. Since it worked for the relays I didn't suspect it, until I connected my nice new run from the battery (dressed and routed quite neatly I might add) and ended up with the same 1.6V.

A quick check with the DMM showed only 11.1V through the chosen ground point.

Oh well, the important thing is that it's all working now. posted_image

Thanks for the suggestions!

Posted By: KarTuneMan
Date Posted: April 15, 2007 at 12:25 AM

AH HAAAA.......rotton grounds. I hate it when that happens. Good work with the troubleshooting.

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