toyota rear window defroster triggering?

I was wondering if anyone here is familiar with triggering the rear window defogger and mirror heaters in a late model Toyota(2012 4runner)?

I have already found the two switched ground wires inside the cabin that lead straight to the factory relays in the engine bay. The factory relay coils appears to operate with a constant +12 volts and a switched ground.

However, I took a precaution before I started tapping into the factory harness and measured these ground signal wires with a DMM while car is running.

It turns out that when the defroster/heaters are not activated there is a constant +12 volts on the ground signal wires while the car is on. If I activate the defroster/heaters via the factory button the ground signal wires then drop close to 0 volts.

My question is would it be safe to apply a latched ground signal to these ground signal wires with the constant +12 volts across the lines?

I would be applying this ground via another relay, this relay being triggered by the remote start's defroster output signal.

I also verified that these are the correct pins using DEI's wiring guide for my particular vehicle, and DEI also lists this as a latched ground signal.

But of course you can never be too safe with electronics. After all, once you let the smoke out of the circuit, you can't put it back in

Thanks very much for any help you guys can provide!

You don't need a relay to trigger a relay. The output from the remote start connected straight to the trigger wire is all you need.

Oh I am actually trying to activate 3 relay coils at the same time isolated by diodes, so I thought the current to drive 3 might be a bit too much for my 200 ma output? I believe the remote start manual lists the max ground current on the defroster output as that?

Also, what do you think about there being the +12 v on the ground signal wire while the relays are not active? I was thinking it might be some kind of inline pull up resistor (inside the a/c ecu) to help protect from surges but I am not sure.

Do you think it is safe to apply ground with the a/c ecu plugged in and running?

Thanks very much for your help.

If you are triggering 3 relays, then you would want to use a relay and split the output with 3 diodes. Don't work about the +12v. That is the other side of the relay coil you are measuring.

Oh right, that makes perfect sense about the +12v passing through the relay! And yes, I shall use a relay and 3 diodes to isolate as suggested. Thanks very much for your help again and have a great holiday.