If you don't mind running the risk of leaving it switch on and draining the battery then perhaps this might work, but I'm not 100% sure:
You could buy a cheap hardwire kit for less than $10 on Amazon and run two separate feeds into it using add-a-circuits. You have to use the hardwire kit and not wire directly otherwise you'll be putting 12V straight into the dash cam which will fry it. If you want to go ultra cheap then you can wire into the cigarette adapter that comes with the dash cam by unscrewing the end and tapping into the relevant parts, we've done this for a trial but it's not very attractive or secure.
- One feed from a fuse which only comes on with the ignition
- One feed from a fuse which is always on and put the inline switch into this circuit
Both circuits will feed the hardwire kit whilst running the car but the hardwire kit will regulate the output to the camera automatically to 5V and 1.5A. When you switch off the ignition the feed from the always on circuit will still be live but whether or not it allows power into the hardwire kit and onwarwds to your camera will depend on if the inline switch is set to on or off.
So all you need is the following which should be doable for around $15 all in:
x1 Hardwire Kit (12-24V input type)
x2 Bullet Connectors
x1 Butt Connector
x1 Ring Connector (not 100% necessary but neater and more secure for connecting the ground)
x2 Add-a-Circuit (either mini or regular sized blades depending on your car's fuse box)
x1 Inline Switch
x2 pieces of wire that can handle say 5A (speaker wire can be used)
I'd recommend having a multimeter to hand to test outputs at the various points but it would be really good if someone with electrical knowledge could verify if this would work or if it's going to fry the hardwire kit or if it simply won't be able to draw the current properly due to the split? The add-a-circuit fuses will protect your car OEM circuits and the hardwire kit has an inline fuse which should protect your dashcam and also the hardwire box so it should be safe, I just don't know if it will actually work though.
I think the voltage will be in parallel so it should stay at 12V but even if it's in series it will only be 24V which the hardwire kit can handle. I think the current would double if in parallel (remains the same in series) but that shouldn't matter either because of the hardwire kit. Or I could be talking total crap here? lol
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