12v constant source

Is it generally considered safe and good practice to use the 12V constant located in the ignition harness to power (with a fuse) the Alarm\RS?

As long as it supplys enough amperage for your application.

And if you know your vehicles you don't even need the fuse, e.g. Hondas which have a 50amp fuse in the engine bay fuse box feeding the ignition switch.

I have to disagree with you on this one Howie. Although it is possible to not use the fuse, by not using a fuse you are setting it up for possible failure. If by some slim chance the unit were to short out, one of 2 things could happen. 1) The factory fuse blows, leaving the person completely stranded and risking the possibility of having the car shut off on them in the middle of a highway when the ignition loses power. 2) The factory fuse is a higher amperage than the ground wire of the unit can handle. In which case the ground wire can melt or burn and possibly cause significant damage. I ALWAYS fuse the constant input and when possible (the cars that I know) I try to replace the fuses in the unit with lower amp fuses than the factory so that the unit's fuses would blow before the vehicles'. Just my .02Kenny

Owner / Technician

KKD Garage LLC

Albany, NY 12205

Don't even know why I posted that one Kenny, being a chancer? In my defence, I do find out whether or not there's an existing fuse/es or link covering the ignition key. Second there are testing tricks that I would never recommend to any one but a serious pro with diagnostics, vehicle specific electrics training experience. I've done courses with DEI techies where we've all used Snap-On bulb test lights but I would never recommend its use to a newbie. The fact is my or your experience knows when and when not to use one. In fact on non-data circuits I will always use the Snap-On over a DMM because it's easier and faster. In fact when triggering lock/unlock it's better because the current required to trigger the lock is about 100milliamps and the bulb does that. Far safer than taking a piece of wire and shorting it to either ground or 12v+. Having said that some cars have more than one constant. On some US vehicles the second may only be 10 amps. In which case I would go for the fuse box battery input. I also LOL keep a few of those Honda 50 amp fuses in stock.

Good Day All. Just my two cents. I know I'm not a veteran in the field by any means, but since the12volt caters to both new and seasoned installers, my suggestion is to always fuse a constant 12v connection whether it's an alarm or remote starter regardless of whether it's from the ignition harness or the battery directly. It costs way less to add that fused connection than to replace possibly melted wires or a factory blown fuse/fusible link.

You're absolutely right, I withdraw my daft statement.

Funny, Howie's #1 made sense to me... But I now concur and agree with all of you. Though one comment (offroadzj) "The factory fuse is a higher amperage than the ground wire of the unit can handle. In which case the ground wire can melt or burn and possibly cause significant damage.Absolutely correct, but that should be covered by the unit's own fuse. But if the unit expects YOU to supply the fuse... (then do!)

Hence my oft intoned mantra about keeping those power lines short. The R/S, alarm and Mr. Parrot are all mounted behind the instrument panel. EVERY wire except hatch, hatch solenoid, yes Kenny I like the idea of a remote as well as a lever and siren + pin switch is less than 18", the grounds are 6". It also means your potential villain can't find anything in a hurry.

Here is one I should have taken a picture of.  Had the pleasure of removing a Ready Remote 24923 remote start unit from a 2008 Ford Focus.  The "installer" connected no less than FIVE tap connectors on the thin gauge Blue/Red +12V constant wire at the ignition harness.  These taps supplied the two power inputs to the R/S, the power for the bypass module, the power for a trunk release relay, and one for a relay to a GEM wake up circuit.  The only fuses used were the original two 30 Amp fuses going to the R/S.

As previously pointer out, only connect ( soldered connections, please ) to a suitable +12V constant source

capable of supplying the current needs of the added equipment.  Fuse all circuits with appropriately ratedfuses.  All ground connections should be trimmed to length and have terminal lugs ( rings ) soldered on.

Soldering is fun!