Which conductor to switch in automotive wiring?

[Captain Dirty]

I disconnected the back-up alarm on my tractor and plan to control whether the alarm is enabled using a toggle switch on the dashboard. For a circuit it makes no difference if the hot side or the ground side is switched. I have been conditioned never to interrupt the grounded conductor in house wiring, but someone suggested putting the switch in the ground wire. Is there any compelling reason to do or not to do that?

 

[prichard]

I'd stick with switching the hot. For troubleshooting I often connect one lead to chassis ground to test for hot. So switched negative would lead to head scrathing.

 

[jaydee325]

On a simple 12 DC circuit, switching the ground will work and I've seen it done.

Having said that, I agree with prichard, stick to switching the positive lead to the load. In looking at my motorcycle electrical schematic, there are loads you could switch the ground, but pick the wrong spot and you could be switching undesired loads and maybe cause damage where electronics are involved.

 

[Xfaxman]

I'd stick with switching the hot. For troubleshooting I often connect one lead to chassis ground to test for hot. So switched negative would lead to head scrathing.

My Polaris EV UTV doesn't use frame ground. So when troubleshooting any machine, the first check should be frame to battery positive post, not the cable clamp.

 

[Rebeldad1]

Its simple to get a answer on this. With the key on pull the plug on your alarm. Check to see if there is power and ground to the plug. No power? put the switch in the power wire. No ground but has power put the switch in the ground wire. And yes... there are circuits that operate both ways. This way it will be operational just like factory.

 

[Texasmark]

I disconnected the back-up alarm on my tractor and plan to control whether the alarm is enabled using a toggle switch on the dashboard. For a circuit it makes no difference if the hot side or the ground side is switched. I have been conditioned never to interrupt the grounded conductor in house wiring, but someone suggested putting the switch in the ground wire. Is there any compelling reason to do or not to do that?

On 12v wiring really your choice. On house wiring it's an accident waiting to happen due to the voltage available.....both have essentially adequate amperage to back up their voltage, but considering the body's resistance value (finger to finger....through the torso) 12v can't defribulate the heart like AC house power can....I think 200 ma through the ticker is the magic number.

Usually designers interrupt the power lead whenever possible. Saves on accidental short circuits on the receiving end.....aka you disconnect a load (wire terminal) from a power source and the lead accidentally falls to the chassis of the unit. If the circuit connected to the wire is also at ground potential, no biggie. If the other end is at power, could be a very biggie.

 

[Industrial Toys]

Just for input. I sometimes switch the negative. For instance in wiring up very delicate wiring to install a rocker switch atop an SCV control lever for Harley rake control, I choose to power a small relay that had keyswitched +12 and then switch the ground. IF there was a short, then the worst that happens is that the relay is on all the time, and I would determine that in a hurry, rather than a blown fuse and everything is dead, and replacing the fuse, would just cause it to blow again. Good, as long as unintentional operation isn't a safety concern.

So, I might just switch the backup alarm via the ground. If the wiring fails and comes in contract with ground no biggie! The backup alarm would just junction as usual. On the other hand, if the alarm is switched from some module and you short the (+) output to ground, you may blow it up.