constant 12v drops to 1.6v

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?

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.

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.

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. Thanks for the suggestions!

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