When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Can be done with a diode and wire connected between the dome light and map light. I've done this on two of my cars (not on my ES yet) it requires you to partially drop the headliner.
Result is dome and map come on with door open, if you turn on the dome light via switch the map light also comes on or if you turn on the map light the dome light also comes on.
First of all. I need to make a big fat disclaimer - I have only tried this system on a couple of LEDs and a breadboard I've had laying around, I have never tried applying it to the car, neither am I going to try, since personally, I don't see a whole lot of point in it.
From the schematic (which can be found here) it seems like both Dome and Map lights are controlled by Ground, with a constant 12V supply; Dome light is controlled by the ECU once it is switched to the "Door" position. There are two ways you can go about it - with and without triggering Dome light when you switch on Map light. The first one is the simplest, since it basically requires one wire to go from Dome to the Map light.
The other method is trickier, you will need either a relay or a MOSFET to act as a switch. For the relay, connect one end of the coil between ECU and the Dome light, and the other one to constant 12V supply. As for the switch portion, connect one end of a normally open switch to Ground and the other one between a Map light and the Map light's switch. Now when you open the door, the ECU will supply Ground to the Dome light and the Relay, therefore switching it on, which in turn supplies Ground to the Map light. Once you close the door, and turn on the Map light, it does not trigger the relay, therefore Dome light will not switch on. If you will both open the door and turn on Map light, nothing will happen, since you are basically supplying the same Ground with two wires. The best part about this circuit is that when Dome light is switched to "On" position, Map light won't be triggered, since in that position, the light is powered from a separate circuit.
As for the MOSFET, since the ECU supplies Ground, you cannot just use NPN transistor. While you can use a PNP MOSFET, it will cause a parasitic draw, because of the way it has to be connected, so a better alternative will be to use a PNP Transistor to supply Ground to an NPN MOSFET, that way no power will escape until either one of the switches is triggered. Only use MOSFET, since regular transistors don't like carrying big loads. The basic principle and the functionality is the same as for the relay, it is just that this time transistors are used as switches, which is quieter, more efficient and more compact.
P.S. For the life of me I can't work out why do you need a diode in the first method.. There is a way to do the same thing as the one described above with just a diode and a resistor, however, it will be very bulky, grossly inefficient, and will result in one light being dimmer than the other. That said, I wouldn't call myself a professional electrician either, so I would really appreciate any corrections you can make.
The diode prevents power from leaking back into the integration relay and whatever is connected to the dome light circuit such as the illuminated key ring. There is no need for any extra components outside of the diode.
BTW when using a MOSFET in this application you need to put in a 2-4 ohm resistor in line with it what it powers, the internal resistance of a MOSFET is very low so if there is a short it will instantly fry the MOSFET even before the fuse blows.
That looks great! I was also thinking about using diodes, but schematic with relay looks pretty good. I'll stick to it. Now hopefully I can fish wires above the headliner without removing it and get relay and connector for it from picknpull, the small one like GM style should work. The big surprise is that my friends 2000 Avalon have that option and 02 Lexus does not.
Thank you for the advise
The diode prevents power from leaking back into the integration relay and whatever is connected to the dome light circuit such as the illuminated key ring. There is no need for any extra components outside of the diode.
Well, that makes sense, though in my defense, in 4th-gen ES, those lights are no longer routed through the integration relay, they go through the ECU, hence why I've had hard time figuring out what that diode is there for.
Originally Posted by Lexus2000
BTW when using a MOSFET in this application you need to put in a 2-4 ohm resistor in line with it what it powers, the internal resistance of a MOSFET is very low so if there is a short it will instantly fry the MOSFET even before the fuse blows.
As for the resistance, it is a good idea, though it depends, since if the MOSFET itself will get shorted, there is nothing that can save it, but in other cases, wouldn't the light bulb serve as that resistor? There are some very effective shortage protection systems already available for MOSFETs, like some newer ones with built-in overcurrent and overheat protections (and they are surprisingly cheap), or even something simple like a PTC Thermistor should also work out..
Well, that makes sense, though in my defense, in 4th-gen ES, those lights are no longer routed through the integration relay, they go through the ECU, hence why I've had hard time figuring out what that diode is there for.
It still works the same way. The MOSFET circuit you came up with is doing the same thing as a diode since a MOSFET or any transistor is a switching diode. You made a switch for a circuit that already has a switch, the ECU or integration relay why do it twice? Just protect them with a diode and done.
As for the resistance, it is a good idea, though it depends, since if the MOSFET itself will get shorted, there is nothing that can save it, but in other cases, wouldn't the light bulb serve as that resistor? There are some very effective shortage protection systems already available for MOSFETs, like some newer ones with built-in overcurrent and overheat protections (and they are surprisingly cheap), or even something simple like a PTC Thermistor should also work out..
The resistor is for when people are replacing the dome light with the door open (power to the socket) and accidentally short to ground. It will save the MOSFET. Integration relay has a low ohm resistor for this purpose.
10-16-20, 10:49 PM
