Interesing Question? - for all the wiring experts

[pipes]

When you are wiring up anything (be it neons, subs etc) and you have them running through a on/off switch..
My question is
Do you switch out the ground or power?
I have always switched out the Power.. Apparently this is not the best way to do it..
Also when working on the electrical system on the car do you disconnect the Ground or Power from your battery?? apparently it is the ground on this as well..

Give me your thoughts.. It was something I never considered..

The reason this has came to question is that I was trying to hook my neons up to turn on when the car door opens.. I could not find a power source.. As it turns out the wires running to the little button is just a switched earth, now Power!!!!

[rancid420potheadpunk]

i havent really paid the much attention to whether its the power or negative at the switch. i disconnect the battery and take it out of the car, had a bad situation one time.

[guyaverage]

Technically speaking the ground (-) IS the power. Electrons flow from the battery negative (-) terminal to the car chassis (ground), thru the load (the lights, stereo, whatever) and back to the battery thru the (+) lead (this is known as the electron flow theory.. there is also a "conventional flow theory" which states the electrical flow is + to -, but since electrical power is in general the flow valence electrons (-) it is accepted that electrons flow from an area of high electrical charge (-) to an area of less electrical charge (+)). In the case of hooking up accessories, you want to put the switch into the (+) lead (the red wire). If the switch was in the ground (-) side, since the car chassis is ground, and most accessories 'chassis' are ground, if the 'chassis' of the accessory touched the body of the car (which it will inevitably do) the circuit would be complete and it would turn on without the switch, since the switch lead would just be a redundant ground.

When working on anything electrical, you want to disconnect the ground (-) black lead from the battery first. NEVER disconnect the red positive lead from the battery without disconnecting the negative (black) lead first. If ANY part of your wrench is touching the positive lead and any part of the frame or body of the car, you will complete a very low resistance HIGH amperge circuit and your wrench will spark like mad, heat up red hot,weld itself to the frame and battery terminal, and probably destroy the wrench, battery, terminal, negative lead, and possibly you in the process.

[pipes]

Hey man thanks for the run down on Electronics 101.
Being an Electrical Engineer I knew the basics and agree with what you said.. Just couldn't figure out why the oem wiring used switched earths..
Thanks for your reply I am sure that this will help alot of newbies on the wiring of anything

[curtklze]

I have to counter a little.

If you switch the power (with out a relay), so the switch is supplying power to your device, then ALL the CURRENT will be flowing through that switch, thats not the best idea if its a small crappy switch supplying a high amp consumer like a power window motor.

If you switch the ground side (like most manufactures do) then the device will use all the power and there will be only a VERY small ammount of electrons flowing through the switch to the ground.

Injector are switch by ground in the ECU, MOST import cars use ground switching for power windows, and door locks.

Most blower fans(what blows the air from your vents in the dash) have 1 big B+ power wire going to the motor, then to control the speed the switch will switch between different ground wires with different sized resistors in them, this adds different ammounts of resistance into the circuit making the fan blow slower or faster.

GM and Ford Used power side switches for their power window switches for a LONG time, but there switches went bad alot and they were VERY big with very big terminal connectors for all the power to flow through.

Basicly switching the ground side of a circuit put less strain on the device and the switch and the entire circuit.

[guyaverage]

If you switch the power (with out a relay), so the switch is supplying power to your device, then ALL the CURRENT will be flowing through that switch, thats not the best idea if its a small crappy switch supplying a high amp consumer like a power window motor.

I agree, if installing high-amperage draw accessories its always best to use a relay.

If you switch the ground side (like most manufactures do) then the device will use all the power and there will be only a VERY small ammount of electrons flowing through the switch to the ground.

Problem is, current doesnt flow TO the ground, it flows FROM the ground.

Basicly switching the ground side of a circuit put less strain on the device and the switch and the entire circuit.

True, in automotive circuits, is preferential to switch the ground (-) side, but not always practical.

Some ciruits switch the - side, some switch the + side. Switching the + side will reduce the life of a switch because it will arc when opened (if the voltage is high enough in that circuit...there is a long drawn out reason for this). Problem with accessories is, since the chassis of the vehicle is negative ground, you HAVE to switch the + because the body of the accessory is negative ground also and putting the switch in the negative lead will be a parallel ciruit, and if the chassis of the car is touching the chassis of the unit, you will have a permanent "on" condition. In this case, even though is isnt preferential to switch + , its 'required'.

<small>[ December 11, 2003, 03:01 PM: Message edited by: guyaverage ]</small>