Light Bar Wiring - Help

[woodman60]

I've read numerous threads, which is why I thought I know what I was doing, but clearly not yet.

Somehow I think my relay is on when it should be off.

I have a wire from the positive battery terminal to an auxiliary fuse box. Pin 30 (red wire) is connected to the fuse box. Pin 87 (blue wire) is connected to the light bar. Pin 85 (black wire) is connected to chassis ground block. Pin 86 (white wire) is run through the firewall to an AOB switch. Pin 87a (yellow wire is unused).

When the power is connected the light bar lights up. Doesn't matter whether the switch is on or off, or even connected. Shouldn't my relay circuit be open until it is triggered by pin 86?

What did I do wrong?

 

[swampdodo]

From your post, you appear to have 2 pin 87...actually, it should be 87a and 87...I bet you connected your light bar to 87a...which is normally closed...meaning that it is connected to pin 30 when the relay is 'off'.

I bet if you turn on your switch, the light will go off.

You need to make sure you are on the right pin 87...not 87a.

You have a 2 pole relay.

This should help...

https://www.delcity.net/documents/automotive_relay_diagram.jsp

and some good info here...

https://www.the12volt.com/relays/special-relay-applications.asp

 

[swampdodo]

Just wondering if your relay is 'backwards' from convention...if so, then connect your light bar feed to 87a instead of 87.

Just thought of this as I've seen some strange product come from overseas...

 

[Bumbo]

Nothing to add other than I agree with the above… often times on a Bosch style relay, there will be two contacts… normally open and normally closed.

You most likely just need to switch the output pin.

 

[woodman60]

updated

My original post is edited above. The light bar is connected to 87, not 87a. However, the switch works opposite. Engaging the switch turns OFF the light bar.

I must not fully understand things. When the light bar turns off, I have no voltage in the 87 circuit, but also no voltage in the 87a circuit.

Help!!

 

[Bumbo]

It’s working, but its working as energized to open, which pulls current from the battery to turn the light off (not ideal).

It obviously depends on the wiring harness and relay, but the import ones I bought in the past had black and red swapped with was very annoying for me mentally. I have no idea what you have or bought…

Looking at my old notes, this is what I had written down.

RED (30) - Fused Battery Connection
Black (85) - Ground (Can be shared with Load)
Blue (87) - Load or Accessory to be switched
Yellow (86) - To Switch (12v + to switch)

 

[woodman60]

Solved

Two lessons learned.

1. Never assume.
2. Don't make permanent connections until you check.

I assumed the wire colors on my relay harness matched the diagram they included. Wrong. Once I closely looked at the harness and the relay pins everything worked fine.

Thanks for helping me think through this.

 

[swampdodo]

If it came from 'overseas', it's not that uncommon.

Glad you got it figured out.

 

[Bumbo]

Glad you got it sorted out.

I know a lot of people are not really setup for this sort of thing, but I always bench test my electrical components before install… it allows me to test the component to make sure it even works, and helps simplify more complex troubleshooting issues.

 

[woodman60]

Glad you got it sorted out.

I know a lot of people are not really setup for this sort of thing, but I always bench test my electrical components before install… it allows me to test the component to make sure it even works, and helps simplify more complex troubleshooting issues.

Amen...a little extra time up front can save a lot of time in the middle of a job.