Hi Guys and Girls,

Probably a really simple question, but I'm new here so please go easy on me.

Using a relay to switch negitive trigger to positive trigger. Only problem is the forward current through the coil when the relay isn't energised. Please how can I stop this?

Thanks in advance

 

How can there be any current through the coil when it is not energised ?

Les.

 

How can there be any current through the coil when it is not energised ?

Les.

Hi Les,

My problem is this. The negitive trigger is coming from a Body Control module for a reverse light. When the trigger wire from the BCM is not being used i.e. Not in reverse. The lamp is allowing the current to flow down the trigger wire and activate the BCM.

I figured that a relay would stop this. However what seems to be happening is the current from pin 86 is flowing through the coil as to 85.

 

How is the coil getting current on pin 86? If the BCM is not energised, how does the relay get any current? Can you draw a diagram of what you have?

 

Thanks Guys,

I appreciate the help!

 

So you're saying when the Bcm wire is "High" the relay is passing current??

Only suggestion is the Bcm pin uses a lower supply voltage like 5V, this is the only logical answer.

 

Yes that's correct, the trigger from the BCM is redundant until reverse gear is selected then gives a very week negitive. so the continuity between 85 & 86 via coil is enough for the BCM wire to be live and rest.

 

Is this how the car was manufactured or have you or anyone else modified it ?

Les.

 

Is this how the car was mnufactured or have you modified it ?

Les.

No it's an addition as the BCM is faulty. It's getting its negitive trigger from the reverse gear switch, but its not putting out a positive to activate the reverse lights. Therefore I'm trying to use the negitive trigger to the BCM as the switch wire. But keep getting this forward current issue. Either direct through the reverse lamp or via the relay.

 

So why don't you use the reverse switch to feed the relay Negative, and then the relay can work the lights?

 

Don't know how it is in your situation, but most ECM and I suppose BCM use a low side switch/mosfet because it is easier than a high side. Why do you expect a positive out put from the BCM?

 

The way you have drawn this would suggest that the BCM pulls to ground when it sees an input from the reverse sitch. If that is the case, you should see battery voltage going to the BCM from the relay but no current flow until the BCM activates the ground circuit. That is not backfeed. If there is cuurent flow, then there is a problem with the inputs or the BCM.