12v to battery or not, remote start

Hey all,

This weekend i'm going to install a R/S (autostart 1755) and bypass (idatalink) in my 07 Ford Sporttrac.  I've been searching around regarding the 12V constant feed.  Some say I should run from the Bat and others say it's fine.  The 12V constant in the ignition harness is only 15amp.  I've been flipping through my Ford DVD and the blower motor and starter are both run off relays which means i'm really only powering relays with my remote starter.  I'm going to use the -12v output for the parking lights to keep the current down too.  I should be fine to wire the 2 12v bat leads and bypass to the ignition harness right?  I intend on replacing the 30 amp fuses with 15's too since that's what i'd be limited to.  I also don't like the thought of trying to run more current through factory wires that are only designed for 15amp anyway.

I'm just trying to provide a solid explanation since some of them are confusing to say the least.

I've never bought in to the 'lose security' arguement.  If a thief pops your hood and does not find an alarm power wire they can still cut the main power wire to the battery, rendering the system useless regardless of how it is connected.  They would then have time, with the alarm dead, to disable the alarm before reconnecting the battery.  No offense Howie, but most installers that are against wiring to the battery are actually against the extra work involved.

If your 12vdc power wire is only fused at 15A then there really isn't a point to dropping the fuses down from 30 to 15.  Those fuses are to protect the wiring, which is capable of carrying 30A per wire.  If you drop them down to two seperate 15A fuses that is still 30A of capacity because the fuses are in parallel.  So, you won't limit the current of the remote start to the factory 15A fuse.  It won't hurt anything to drop them down, but it won't help you the way that you think it will. 

The one thing to keep in mind when using the main battery wire under the dash is that if anything goes wrong with the remote start it is possible that it will blow the main factory fuses.  On my G35 the factory fuse is NOT an auto parts store fuse, it is a dealer order fuse that costs $15 and takes two days to get.  You do NOT want to blow these fuses, especially on a customers car in the bay.  In cases like that you are better off going directly to the battery and fuseing everything with your own fuses.  That way, if a fuse blows you will have the ability to replace it easily, and it won't prevent anything else from working.

I just like the idea of running a seperate line from the box under the hood.  I was going to tap in to the stud before where the main fuse is.  I have to go through the firewall with 2 wires whats one more in the grand scheme of things.  The factory wiring is 15 amp so I figured i'll leave each R/S line the ability to use the factory amperage.  I plan on using the neg triggers whenever possible anyhow.

I totally agree with you Howie.

I've got my power from the igntion wiring in certain cases, but I always prefer going to the battery to achieve isolation from factory fuses, and to provide the customer a quick and easy way to shut off the alarm system in case something has failed.  I just hate the excuse that you are making the alarm less secure by going to the battery because you are not in any way doing so.  If a thief has access to the battery it doesn't matter where your alarm is connected, it can be disabled.