Dome light circuit question

I have a 2009 DC and I would like to wire the light in my cap so that it works with my dome light. Any suggestions as to the easiest way to get to the wire or circuit that goes to my dome light? I had a setup like that on my old Ford and I would like to do the same to this truck.

 

On the drivers side junction box there should be a blue wire in there. That is the interior light. You'll need a meter to confirm it. From there you need to I'd probably power a relay off of that wire to ground. Then wire the relay up to the new light in the cap.

The box is in the window post at the drivers side door. Actually there is a easier way to find it. It also goes to the fuse box on connector number 1E. There should be a solid blue wire there. It's the bottom right plug. Pin 9 on that connector should be a solid blue wire. Confirm with a meter that it is indeed the interior light. From there tap of that for a relay then run a new fused circuit to the new cap light. Why that way? Cause it will run under the truck a ways so a short is more likely, best keep it separate. Oh and it goes to the body ECU from there so you don't want to load that existing circuit up anymore than it is now so you need a relay.

 

Thanks Trap

 

Been there, tried that! I know for sure that a relay won't work powered off the dome light circuit. When the light fades on and off, the relay contacts chatter. There might be a way to wire a small capacitor in to prevent that, not sure. The wire is really thin, not sure it can support another light wired into the existing circuit.

 

No you don't want to wire up another light off of that circuit cause it goes to the ECU. For the dimming part.

Ok well if it chatters the way to prevent that is use a zener diode inline with the relay coil. The zener diode should be set to 12 volts. that way when the voltage drops below 12 volts the diode will not conduct turning the relay off. Look mom no chatter.

Forget that it's much more complicated than that. You need a bleed resistor too with the zener so you you need to do some math..

FORGET THE RELAY !!

Use this instead:

http://www.eurothermonline.com/product/SVDD-1V12

Don't expect it to work unless there is actually a load connected to it. It will not turn on unless there is a load.

My mistake I should have thought about that damn dimmer part. The blue wire is the positive. so it goes to the trigger positive side the other trigger terminal goes to ground. Then it's just like a normal relay except it's solid state. No chatter.

Basically you can get these things everywhere at any electronic supply store. You just need it to work DC and have a trigger voltage of 12 volts. The contact side is not as important but it should be able to handle conducting 12 volt no problem,

Ask them for something like this:

Continental SSR 12 amp
0 to 100 VDC load voltage
4 to 32 VDC control voltage
1 phase - DC resistive load

If you try doing it with Zeners or transistors or the thousand other ways of doing it you end up with this thing basically so just use a solid state relay and be done with it.

 

Thanks again Trap.

 

I may have to give this another try myself. Thanks Trap!

 

I have about twenty at least of these things in my tool box but there circuit board solder mount so useless for a truck. At least that one has a nice case and wire terminals. If you have some heat sink compound it's a good idea to add some to the bottom when mounting it but chances are just running one light it will not get hot enough anyway. Remember the one I posted the link to is only rated at 12 amps on the load side. Usually they are much larger. Frequency drives use them and sometimes there rated at a 100 amps or more.

Larger is better if you can pick. 30 amp would be perfect. Would never goof up even when the bulb burned out.

Just make sure the load side goes down to zero volts and up to at least 24V DC. The trigger is pretty standard 4 to 32 volts cause it's actually a LED. Light turns it on. There is not physical connection between the trigger and the load.