Making the stereo work with the key in the off position...

wrybread · Post by **wrybread** » 23 May 2019, 00:51

I like to set up my car stereo so I can use it even with the car off, and ideally so the cigarette lighter socket can deliver power too, so I can leave my phone charging. I usually just hook up a switch between the constant 12v+ and the switched 12v+ in the stereo harness, but I did that just now with my SC-816 and blew two fuses...

Can anyone think of a reason for that, other than user error?

I verified the wires with my multimeter and all looked good. No power to the switched line until I turned the key. Other line had power always.

And this diagram agrees with my wire choices:

https://www.tehnomagazin.com/Auto-radio ... nector.htm

Connecting one of the green/brown wires (constant 12v+) to yellow/purple (switched 12v+). In this diagram that's wire 1 and 3.

Post by **BEJinFbk** » 23 May 2019, 08:12

Instead of an SPST switch, use an SPDT.

Connect the common contact to the radio
ign and the batt and harness ign to the two
switched contacts of the switch.

That way, the ign lead from the harness is
disconnected from power when you flip to
batt and there’s no backfeed up the harness.

Post by **wizechatmgr** » 25 May 2019, 02:01

Or install a diode and it will just always have power and never backfeed =)

wrybread · Post by **wrybread** » 25 May 2019, 10:34

That's a good idea. Any recommendation on which diode by chance?

Post by **wizechatmgr** » 25 May 2019, 18:05

My thought is one of these on each power line (aka V1,V2) going towards the radio should do it... They are basically one way valves for electricity.

pardon the garbage schematic no guarantee I have the cathode anode correct, it's just here for purposes of clarity

: radio.png (6.26 KiB) Viewed 976 times

https://www.amazon.com/RUITASA-Schottky ... 4253919969

Post by **abscate** » 26 May 2019, 01:44

The diode needs to be rated for the expected power draw if about 10 watts for the charger, plus 50% margin

Post by **wizechatmgr** » 26 May 2019, 03:09

abscate wrote: ↑26 May 2019, 01:44 The diode needs to be rated for the expected power draw if about 10 watts for the charger, plus 50% margin

Absolutely...
These are rated for 10 amps each. Worst case scenario he uses two or three in parallel for each voltage source.

wrybread · Post by **wrybread** » 26 May 2019, 12:10

Great ideas, will try next week.

I still don't get why bridging two circuits would cause a short or a power draw. I was working by headlamp after a long day so maybe I did something stupid. My plan is to insert two 5a fuses and connect the two lines with a multimeter set on current measurement to see if I see the same power draw.

If it blows that again, plan diode.