Source of +12V in engine compartment

Madartsoft · November 25, 2018

Hi,

I'm trying to install DRL in RX400h and looking for +12V power source in the engine compartment. The power should be only when ignition key is in position ACC or engine on. I checked in fuses box and there is 12V but even if the engine is off.

Regards

Herbie · November 25, 2018

I can't remember the exact fuse numbers but I do remember it was an EFI fuse and remember, this was on an RX300 - the 400h may be different.

You may be able to tell from this photo which fuses I used. If you need a wiring diagram for the two relays I'll draw one out for you, just let me know:

Madartsoft · November 27, 2018

I think in rx400h fuse (marked red) is EFI. It's 10AMP fuse, the relay coil needs 150mA so should be fine I guess. Could you draw the diagram for two relays please?

Herbie · November 27, 2018

Yes, I'll do it tomorrow and post it up for you Sylvester, no problem.

Herbie · November 28, 2018

@Madartsoft Here you go Sylvester, the wiring diagram is below.

With the ignition off, the permanent 12V feed to Pin 30 of Relay 1 is normally connected to Pin 87A so it can't go anywhere. When you switch the ignition on the 12V supply from the EFI fuse goes to Pin 85 of Relay 1, energises its coil and pulls the contact from Pin 87A to Pin 87, thereby providing a path for the ignition-switched supply to get to Pin 30 of Relay 2.

Because Relay 2 is off, this supply goes through the normally closed contacts from Pin 30 to Pin 87A and provides power to the DRLs. This part of the circuit ensures that the DRLs are only on when the ignition is on.

The second part of the circuit makes sure that the DRLs switch off when the side/tail lights are switched on, making sure that no one is dazzled by the very bright LEDs at night. It does this by tapping into the +ve feed to the sidelights and connecting it to Pin 85 (coil) of Relay 2. When you switch the sidelights on, the coil of Relay 2 energises and switches the incoming ignition-switched supply on Pin 30 away from Pin 87A and to Pin 87, thereby breaking the connection to the DRLs and switching them off.

Hope that helps

Madartsoft · November 29, 2018

Hello Herbie,

Thank you very much for the diagram. Partially I manged how it should work but now it will make it more simple. Have you noticed any issues connecting the relay to EFI ??

Thanks and regards

Sylvester

Herbie · November 30, 2018

2 hours ago, Madartsoft said:

Hello Herbie,

Thank you very much for the diagram [...] Have you noticed any issues connecting the relay to EFI ??

Thanks and regards

Sylvester

You're welcome Sylvester, I like to help where I can, and no, no problems whatsoever by using the EFI supply line.