We have a 2012 Prius that came with a standard rear view mirror. I installed a GenTex mirror with auto-dimming and HomeLink. Following the install instructions that Toyota had online I hooked up the Red wire to constant power for the dimming and the other wire for the home link to keyed power. I grounded the ground wire to the car frame. Both functions work with the dimming feature green light on at all times. Yesterday the 12 volt battery was dead and I had to jump the car to start it. I turned off the green light. Dimmming and Homelink are all the features this mirror has. Did the green light kill the battery and should I have connected both wired to the keyed power? It's my wife's car and I'd hate to have her on the side of the road because the starting battery went dead. Has someone who has done this upgrade had this issue? What would folks suggest I do next.
do a quick test. check the 12v voltage in the evening, morning and evening again with the car off. then repeat with the mirror disconnected. maybe it's just a coincidence and you need a new 12v. how old is it?
The battery was purchased in June 2019. It only went dead once before when my wife left the interior lights on for several days. I replaced all of the interior with LEDs. I can't find anywhere how much the green light on the mirror actually draws. Or if I should only use keyed power.
My retrofit runs on constant 12v for almost 10 years. It draws 6ma standby and never caused an issue. But if you have switched 12v run it that way. Its the same as turning it off with the mirror's on off button. My understanding is the Homelink is normally constant 12v and the dimming is switched.
From everything I have read it is my understanding that the HomeLink is switched so no one could have open access to your home any time the car isn't locked. Is this incorrect?
My cars that came standard with homelink always run a garage door when off. The dimming function takes the power and theoretically, if powered, could be activated by a bright light from the rear at night. Just wire both power inputs to switched 12v.
You really should run a parasitic draw test and find out if the car is drawing more than 30ma when shutdown. It takes about a minute to get to the steady state current for the whole car unless you totally disconnect the battery. Then it can take longer as the computers initialize and then go into standby.
That's probably what I'll end up doing. I have two vehicles with homelink. A Dakota and a 330Ci, neither one of them will operate the garage door when the key is off. I'm frankly surprised that your vehicle will operate that way.
Does anyone know if I hook both wires up to the keyed power wire if that would negatively affect the mirror performance?
Normally, they power the Homelink function from a constant 12 volt source so you can use it even if the car is off. But you don't have to. The compass and auto dim function must be powered from a 12 volt source that is only on in the accessory or run mode, otherwise you might deplete your 12 volt battery if it is always on.
Actually I don't know. I followed the Toyota install instructions and it said to connect the red wire to constant hot wire and the Homelink wire to keyed power. I'm going to put both on Keyed power tomorrow. At this point I'm getting quite fast at taking interior parts apart.
I thought I should wrap this up. This morning I connected both Gentex wires to the keyed power wire (light blue) and everything seems to work fine. This should eliminate any drain on the 12 V battery when the car is turned off. Just to check I experimented with our other two vehicles with auto-dim and HomeLink. I got a surprise. On my 2002 BMW 330Ci the key has to be in the ignition and turned on for the HomeLink to function. The HomeLink buttons are on the mirror. On my 2002 Dodge Dakota the HomeLink, which is not on the mirror but in the headliner works all of the time. I live in a very rural area and have never locked my truck which is parked outside. I will now lock it up all the time. For more than ten years anyone could have entered our house using the truck HomeLink. My truck is always parked at least a hundred feet from the garage doors, and it still works from that distance. Not a very safe situation. Hopefully my wife will never be stuck with a dead battery in the Prius again. She does like the convenience of the HomeLink which was the biggest reason to do this in the first place. She doesn't drive much at night so just how well the auto-dim works we aren't sure. My $25 mirror project is complete. Thanks everyone for the information on this now finished project.
The dimming function uses a light sensor facing forward to determine when it is night and a sensor facing rear to determine when a bright light is hitting the mirror. Under these conditions the mirror actually dims (darkens) over five seconds. When the bright light goes away the mirror clears up over five seconds. You almost never notice it although you might realize the guy's brights behind you dims over those 5 seconds. Its almost like the mirror automatically gets a dark tint. You can still see the guy's headlights but lose some of the normal mirror's reflectivity. One way to test is to park in a dark garage with the garage door open. Sit in the car with the interior lights off. Adjust the mirror so you can see something behind you that has some illumination. Does not have to be bright. Power up your switched 12v. The green light comes on. Now turn on your passenger's map light while watching the mirror. The reflected image will get dimmer over five seconds. Then turn off the passenger map light and the mirror will get clearer and the image will be brighter. The maplight is simulating a bright headlight from the rear. During daylight nothing happens as headlights from the rear are not a problem.
Unfortunately the 12v agm batteries slowly go dead. Seven years later you get stranded in a parking lot. A rear hatch slightly ajar will drain the 12v overnight while subtracting a month of battery life. An led bulb in the back is a good idea; leaving it off at its switch is even better. Maybe a new battery every five years regardless if you need it or not. My wife has a Lithium Jump Pack under the seat with instructions on how to use it. Much safer than a jumper cable where a momentary reversed connection results in a tow and a big bill.
