Wiring a master switch, help!

**Kalenth** · 11-30-2008, 05:49 PM

I wired up a master power switch for my system. It is a simple 3 post switch from Radio Shack, with a LED that illuminates red when it is on.

In the house, I wired it where the 12v in line would go to the center post, neg. to the right post, and the 12v out to the left post. When I used an ohm meter, it read a contstant 12v in... and read 12v out when I powered on the switch. You with me? so far, so good.

So from this, I assumed that there was live energy to the plug, that wouldn't go past the plug until it was switched on.

But when I installed it in the truck, I took the 12v from the back of a cigarette lighter and hooked it in the switch, then I used some cable and ran it from the switch to the cigarette lighter, assuming that it would be dead voltage until I flipped the switch.... wrong.

It seems that when there is something plugged in, it pulls electricity no matter what.

Any ideas on how I can wire this up to be a true master toggle, where it cuts of the circuit when I flip the switch?

__////
+ + -
+ + -
+ + -
+ + -
12v 12v neg
out in neg

**bratnetwork** · 11-30-2008, 07:20 PM

Does the light operate properly when you flip the switch? if it doesnt then its wired wrong. If it does work properly then it could still be wired wrong. It is possible that even wired wrong that the indicator light on the switch can pull a ground through the power wire going to the device (i'm a mechanic and i've seen guys at my job do it).

I would check the wiring... sometime on the switch by the prongs there are really small labels molded into the plastic and if you look really close under good light you can read what they say.

**Bugbyte** · 11-30-2008, 07:40 PM

I use this switch in my car as a valet switch. The light is only on when the switch is in the on position. It is a simple single pole, single throw switch with a light in it

I would NOT use it as my master power switch, however. Although RatShack lists that as a 25 amp switch, you'll need to be very careful about what gauge wires you run to it. You can't expect small gauge wires to carry that kind of current.

I use it simply as an interrupter switch. It is inline with the accessory wire, before it runs to the power accessory input on the power supply. When it is off, the pc never starts.

To wire it, you need to use the multimeter to check continuity between two of the poles. You should see it on when the switch is on and off when the switch is off. The other pole should NEVER show continuity to the other two That is your negative pole.

Test in the car in steps. First, get the switch to work by hooking the 12V to it, then the cigarette lighter to the other pole. Test with multimeter - 12v on, 12v off when the switch is toggled.

Then, hook up the negative to the other pole. Test again. 12v on, 12 off and the light should work.

Again, I wouldn't use it as a master power switch, but it's up to you to decide whether it will work.

**Kalenth** · 11-30-2008, 08:51 PM

hmm... well, after I tested it in the house, I went ahead and satered everything together inside, labeled the cables 12v in and 12v out.... but when I hooked it up in the truck, the lgiht never came on.... I am thinking maybe I melted something inside when i satered it... and maybe something melted together. That would explain the light not coming on and the 12v continuing from the switch in the off or on posistion.

**bratnetwork** · 11-30-2008, 09:59 PM

that is possible if it got too hot while soldering it... Just pick up another switch like that and try it out and then just use crimp connectors instead of solder.

**GizmoQ** · 11-30-2008, 10:32 PM

We've been down this road many times before. Try reading through this thread.

I used to have a switch that fed off both the ACC and battery lines (post 1 and 3) to supply power to the CarPC (post 2) and this worked well in my 91 Mustang, but my Caddy uses the ACC line for Class 2 data and was too noisy for powering the CarPC so I came up with this wiring diagram to use with my SPDT switch.

**Kalenth** · 12-01-2008, 09:31 AM

Gizmo... thanks so much!

**dMand** · 12-11-2008, 08:10 PM

if there's no diagram for the LED rocker switch, 99% of the time, the ground wire is the spade terminal directly behind the LED light. The center spade terminal is always your positive out to the component, and adjacent to that power output is your supply "+" input voltage.

The center spade is usually "+OUT". The "ON" position of the switch is the LED side when pressed.