So I always run a radar detector. Until recently, it was windshield-mounted with a suction cup bracket, cigarette lighter power source, and it *always* powered up with the ignition. I recently got the windshield tinted and they advised against suction cup use, so I took the opportunity to fabricate a mount under the rearview mirror, hanging from the shroud around the rain/proximity sensor bank. I tapped 12v power from inside the shroud per a YT video, and it works as expected, mostly. Power is always there when the truck is on, but for some reason I have to hit the power button on the detector to turn it on...sometimes. Other times it powers on with the truck as it did when in the cigarette lighter. WTF? Not a big deal, but the change and inconsistency is really odd. Any thoughts?

 

Make sure the ground is solid.

 

Once it's on, it stays on without issue. If ground were wonky, I'd expect it to stutter a bit, no? I can wiggle the wire all day long without it losing power.

 

Did you measure voltage coming out of that lead with and without and while the engine is turning on? If the voltage is at the border might be a little low when starting and doesn't always wake up the radar detector.

 

I have tapped in to the rear view mirror power at the connector and mine works every time I turn the truck on.

You may want to share exactly how you tapped in. Sounds like a flaky connection or not the correct pins for some reason? Start up current could be higher than powered on current draw.

 

Throw it away and get a new one.

 

The radar detector, or the truck?

 

 

Your problem lies in the modification you've done. Look at it objectively...everything was fine until you did this, correct? So you've got a wonky 12v connection, plain and simple. That's the only thing that changed since it all worked correctly, so...there you go...there's where you start.

 

Power source also changed. Cigarette lighter to shroud. These two could be controlled differently.