Wiring lights thru relay

[Baker7888]

Hey guys, I am trying to wire some aux lights up using a relay and having an issue hopefully can be solved with a different relay maybe. Sorry this is not on a g body but on my pickup, but i have received a lot of excellent wiring help from fellow members so thought it would be ok to ask.

I want to use the cargo light switch to activate the lights but the lamp has power all the time, and the switch completes the ground which turns the lamp on. However when i wire my aux lights I am getting aux lights on when switch off (opposite of what I want)

Wiring is as follows

30 - batt pos
85 - 12v accy switched
87 - positive to aux lights
86 - trigger wire

My trigger wire is hot when i need it to be cold and cold when i need it to be hot
So aux lights on with switch off and aux lights off with switch on

Wondering if i can use a different relay or do i need to start from scratch ??

 

[85Frankencar]

From what I can tell from a Bosch-style relay diagram, I think the 85 and 86 need to be swapped? 85 should be grounded to close the internal relay switch circuit. 86 should be connected to the “on” position of the switch you’re using to close the main power circuit. That way, when you switch the cargo light switch from the “off” to the “on” position, it’ll send power through the 86 circuit, then ground. That’ll activate the internal relay switch which should turn on your aux lights. Hopefully that helps? Been a bit since I’ve had to think about relays…(edited to clarify).

 

[ELCAM]

You are using the ground signal from the switch as your "trigger" wire? It is also connected to the cargo Lights at the same time?

 

[Baker7888]

You are using the ground signal from the switch as your "trigger" wire? It is also connected to the cargo Lights at the same time?

Well, it's hot with the switch off, and grounds (i think) with switch on. One other wire on this switch stays hot all the time and the rest dont do anything that i can tell

 

[ELCAM]

What is the truck so I an see if I can find a wiring diagram for that circuit.

 

[Baker7888]

What is the truck so I an see if I can find a wiring diagram for that circuit.

It's an 04 sierra. I was able to find this which is the switch i am using. Using blue/white as trigger but getting opposite results

 

[ELCAM]

Do you have a rectifier diode handy? 1N1004 or thereabouts?

 

[Baker7888]

Do you have a rectifier diode handy? 1N1004 or thereabouts?

Unfortunately I do not. What are your thoughts?

I am considering scrapping the idea. Instead of tapping into the switch, tap into the light itself and should have problem solved.

 

[ELCAM]

I think what is happening is that the light in the +12V side of the cargo light is enough of a voltage drop that the relay sees a ground with or with out the switch being on.

If you split the blue white wire and install a diode so that the relay cannot see the +12V side it will work as you want.
.................................. Diode
To Switch ------*--------|<-----------------To light
.........................^ Connect relay terminal 86 here.

 

[Baker7888]

I think what is happening is that the light in the +12V side of the cargo light is enough of a voltage drop that the relay sees a ground with or with out the switch being on.

If you split the blue white wire and install a diode so that the relay cannot see the +12V side it will work as you want.
.................................. Diode
To Switch ------*--------|<-----------------To light
.........................^ Connect relay terminal 86 here.

Thanks ELCAM. I found this switch goes to computer which completes the circuit. The light has +12v all the time and computer controls the ground side. So that if switch is left on after key off, it will stay on for 10 minutes then the computer will open the ground side. So i may need to scrap my plan of using this switch unless i wire the lights direct to the factory circuit and use no relay. Guessing that is a bad idea ?