fused 12 volt connections?

I have a basic question I wanted to hear some opinions on from the pros here.

When connecting a relay or low drawing sensor or something along those lines is it okay to tap into a power source (that is already fused) powering another part of your system say like the headlight switch, door locks, window switches or something along those lines.  And, if it is okay would you need to use a fuse where you have spliced into the power source even though it is already fused at it's main power connection.  For example tapping into the power in the door lock wiring to power door lock relays or the headlight switch to power domelight supervision or window wiring to power window modules etc..

Or, should you fuse and run wires to the battery for every relay and sensor seperatley?

Rod

Whenever I add a conection to an oem wire i always fuse it at a lower rating than the oem circuit! The only way I would not fuse an added on component is when i'm replacing the factory unit completely, Example a oem power power lock module that went bad, i would remove the old one entirely but i would re-use all oem connections that would have been fused for that specific circuit, so no need to  be redundant, simply because the new circuit would be replicating the old defective one!

So you would fuse even remote start power connections where you tap into vehicle wiring because I could swear that I saw a post on here some where that said not to fuse those connections.

I have to ask because I am now curious.  Why would you fuse other tapped power connections but not the remote starter tapped power connection.

hawks] wrote:

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hen connecting a relay or low drawing sensor or....

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I have a slightly different way of looking at this, but it involved knowledge and not "playing it safe".

If, say, you need power behind a door for a window module and the stock window power wire is sufficient in size and current, I would NOT fuse the window module in the door.  The last thing you want is to have to pull the door panel off to replace a fuse, when it would be much easier to replace the window fuse in the OEM fuse box if something were to happen.  Now, as a general rule of thumb when doing this, it is imperative that NO vital circuit is tapped (ie headlights, tail lights, ignition, etc).  You can use ACC circuits like windows, door locks, radio, etc, but nothing that, if the OEM fuse would blow, would leave the car unsafe or unable to operate.

A common place to do this is on RF changers (do people still insall those?).  They would always come with their own fuse and we would always connect their 12v and switched wires to the OEM wires behind the radio.  We would always cut the fuses off because the OEM fuses were sufficent and easy to access.

The remote starts we installed came with fuses inline to the power wires and I NEVER removed the fuses.  If something happened to the remote start wiring you wouldn't want to rely on the OEM fuses, because if they blew the car wouldn't operate, and that would be bad!

Many diffrent opinions and some great answers.  Now let me tell you one of the reasons I asked this question.  I am laying out my alarm install and I have installed a domelight supervision relay and a tilt sensor on a flat spot behind the dash bezel.  Lots of room, easy to get to and close to the wiring I need to tie into.  I noticed that the power wire supplying the light switch is 10AWG so I was thinking that it probably carries more than enough power to handle a tilt sensor with a 1 amp inline fuse and the domelight supervision relay without any problem.  I also don't think that it would cause any problems with the lights since the domelight supervision only operates when arming/disarming and shuts off on ignition and the tilt sensor probably draws so little it dosen't matter.  Good or bad idea?