Tell me about negative switching...

I've seen several threads around the site about how some of the electrics/lighting in our Gen 1's are negatively switched. What does that actually mean?

From my (limited) knowledge of circuitry, every isn't every switch just breaking up a circuit that goes from the positive to negative terminals of the battery?

Part of why I ask is this - I have another thread where I'm working to disable my courtesy door lights. I got

Splash Resistant 16mm Power Push Button ON/OFF Latching Switch w/ 12V Blue LED Power Symbol Head from U.S. Solid

this switch on amazon, and I want the switch to illuminate only when "on" - basically when the doors are opened and the courtesy lights are on (unless I've turned the switch off; then the lights and switch LED would both be off, obviously).



I'm inserting this switch in the kick panel, by cutting the single wire to the door switch, and running the brown wire in the diagram above to the switch, and the red wire to power.



So, while I wire it as shown in the diagram above, the LED on the switch never illuminates, though the courtesy lights are switched, as expected. Is that due to negative switching, or something else?

Thanks,
turbodb

 

in short, anything that is negatively switched is controlled by applying the ground side to the "load".

Positively switched circuit
the switch is before the "load". the circuit is already grounded and the switch is controlling the 12+ volts to it.

Negatively switched circuit
the switch is after the "load". the circuit has 12+ volts through the "load" and up to the positive side of the switch. the circuit is complete when the switch is activated and it provides the groundside.
*you must be careful of this type of circuit. you have a live wire that only needs to be grounded. it is easy to short out or leave something constantly on.

on the switch, you need to tie pins "+" and "C1" together and wire it to input from the fuse panel *hotside*

you need to tie pins "NO1" and "-" together and wire it to output to the door switch.

by doing this, it will allow the circuit to be complete for both internal switch circuits and light up properly. i assume they use an led in the switch so you need to make sure the ground side it going to the door switch. led's like to only light up one way.

 

Very nice explanation, thanks @fergyz ! One more question - with the wiring you describe, does that get the LED in the switch to light all the time, or only when in the "on" position? (I'm hoping the latter)

 

it should only work when the switch is on.... however, if for some reason the light it not tied to the "on" position (internally) it will still only light up when that door is open.

 

Well, gave this a try today and unfortunately the switch ended up lighted when in the "off" position (so the courtesy lights wouldn't light) and dark when in the "on" position (when the courtesy lights come on when the door is open).

I think this may be some weirdness with these switches and their interaction with the courtesy light switch... thinking I may just go with never having the switch light come on (because it does correctly interrupt the courtesy lights when in the off position).

 

Well I think I may need to rethink this one... I did see the reviews mention that the diagram they had was wrong. Wish I had the switch in front of me.

 

@fergyz - sent you a PM...we may be able to work something out if you want to try to figure out how to get this to work w/the door courtesy switch

 

replied