Relay on Dome light supervision

Depending on the vehicle, the domelight may be able to be triggered by a few different methods:

1) Grounding the door trigger on a (-) trigger system

2) Providing the door trigger 12V+ to a (+) trigger system

3) Grounding or providing 12V+ (whichever it is looking for) to a "Domelight" wire, which is just a factory trigger wire that goes to or from the BCM in order to turn the domelight on.

In any case, it is advisable to use a relay to convert the typical 200mA (-) output from the alarm's domelight output into the correct state for your particular application.  If you have ever seen a domelight supervision output connected the lazy way, where you send the output from the alarm to a (-) door trigger output in say, a Honda, you will notice that the domelight does not light up all the way, since the (-) from the alarm is not sufficient to trigger it correctly, not to mention there is a possibility of frying the alarm module by connecting it's feeble ground output to a circuit that is looking for a higher current (-).  The relay is basically using the 200mA as a (-) pole input at "85" where 12V+ is at "86" and sending the appropriate output (12V+ or GROUND) to your domelight trigger input or a door trigger in cases where it is recommended instead, as with most imports.  Many Ford's, however have an actual "domelight" wire that when triggered with 12V+ they light up the interior lights as well as running board lights or others, such as the case on their SUV's.  Hope that helps explain things!

I know this post is old but it's not locked yet, so I was wondering if you could use a relay w/ the domesupervision wire to power cold cathods and leds the only light up when the dome light is on?