Help, using the dome light power as a control signal to a relay.

[DakarTJ]

I am using the courtesy light circuit as a control signal to a relay. The relay will power my rock lights. I am doing this so when I open one of the doors the ground is lit up. It will come in handy at night trying to get out of the jeep. I got it all working so the open door will trip the relay or a switch when the doors are closed.

The issue I have is the Jeeps slow dimming of the courtesy lights when the key is out of the ignition (this is normal). The Jeeps signal to turn off the courtesy lights is a rise from 0.0v to 12v. This slow rise in voltage causes my rock light relay to shudder from about 3v to 9v where it latches. With the key in the ignition the fade does not happen so all is good that way.

I tried to fix this with a 1N4742A, 1-Watt 12v Zener Diode. My thought was the 12v reverse breakdown voltage would stop the rise in voltage from getting to the relay until it hit 12v; then break down and let the current pass to the relay. This did not work. I think the current might not be adequate to push the diode into break down; or the voltage loss across the diode will not let it get to 12v.

The door switch acts the same way in the jeep. The whole circuit runs backwards from the rest of the Jeep. 12v to turn off the lights and 0v to turn them on; I can't find the part of the circuit that's before the dimmer. I think its logic in the computer.

Sorry this is so long, but can you help. Is their a better diode to use?

 

[Eric S.]

Seems like you are taking the power to the relay after the capacitor or dimmer module? If you connect before this should fix your problem.

 

[DakarTJ]

Seems like you are taking the power to the relay after the capacitor or dimmer module? If you connect before this should fix your problem.

I thought about that, but I don’t have a schematic of the circuit.

 

[HenryJ]

Why not just tap the door switch?

 

[motomech]

X2 on that one.

Cool idea for the rock lights acting like courtesy lights.

 

[DakarTJ]

The door switch acts the same way in the jeep. The whole circuit runs backwards from the rest of the Jeep. 12v to turn off the lights and 0v to turn them on. I cant find the part of the circuit thats befor the dimmer. I think it's logic in the computer.

 

[rickc]

If there is a discreet fuse for the internal lamps (there should be) you could tap into the fuse box using a fuse tap. This will provide you with the full 12v switched power for the relay.
http://www.bussmann.com/images/3c2dce34-cf0b-43a1-aabf-d886ccd13aad.JPG

 

[DakarTJ]

If there is a discreet fuse for the internal lamps (there should be) you could tap into the fuse box using a fuse doubler. This will provide you with the full 12v switched power for the relay.

Thank you for your input.
If you are talking about the door defeat fuse, from what I was able to see using my VM; it is also after the dimming circuit. So I still get the slow rise in Voltage. The circuit only dimes when the key is out of the jeep. I either need a point in the circuit before the dimming circuit, or a way to stop the voltage rise at the relay and only pass 12v.

 

[StumpXJ]

Add your own door plunger switch, and have it trigger the relay. Could have it up DC-. But it would work, and would leave your OEM dimmer system alone.

~James

 

[BBsound]

You may be able to use a timer relay like this one: http://ecatalog.squared.com/fulldetail.cfm?partnumber=9050JCK23V36

It might be a little pricey, but it would give you the ability to keep the lights on for a period of time after you get out and shut the door.

They use a constant power feed, (obviously) and you would use the existing dome circuit to excite this relay. once it is excited it will stay on for the determined amount of time.

 

[Jeep]

If it's a JK your issue is contolled by the IPM (integrated power module) which controls a pile of body electrical funtions, I don't know of a way around it either. The separate plunger sounds good, might prevent damaging the IPM (I did that once with trailer wiring problems).

 

[DakarTJ]

You all have some good ideas; my Jeep is a 2001 TJ. This dimming is a normal function of the circuit. I was looking for some electronics experts to chime in. What I am looking for is a way to block the slow rise in voltage until it hits 12v, and then let it pass to the rock light relay. From what I understand a diode in reverse should do this.

 

[DaveInDenver]

Run the tap from the dome lamp through a Schmitt trigger, that would fix the relay chatter. Look up something like the 7414, should be cheap. Depending on the circuit you might have to double up the Schmitts to get the right level. It'll be sorta like this, without the photo detector though and corrected for supply voltage (a 7414 will only want +5V supply). A reversed Zener is only going to guarantee that the level never goes above 12V, but with it your relay control will still track the 12V as it comes up and it's chattering because it can't decide to be high or low when the supply is high enough to activate but not high enough to hold the contacts.

View attachment 26680

 

[ChrisInVT]

The rock lights doubling as courtesy lights is a really cool idea, I might just have to steal that idea from you

 

[DakarTJ]

I love it. If you have an older rig you should not have the problem I am hiving. My system works, they com on and off with doors. It's just the chatter on the rock light relay that bugs me.