how to make the stereo stay on with key out?

[92gsxbafaro]

So on newer cars i like how you can have the key out of the ignition and have the stereo stay on untill a door opens, so i figure why not do it on a 1g.. im just looking for advice about how to do this. any help would be awesome thanks!

 

[VR4 Kev]

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Have revised the diagram one again. The diode is pointing the right way now.

In this version the key turns ON left relay so the door does not affect anything, the key also turns ON the right relay, making it go into a loop while turning ON the radio. With the key OFF the radio and right relay will stay ON untill a door is opened, grounding the right relay and braking the loop, turning everything OFF. Key overrides the door so if a door is open and the key is turned, the radio will be turned ON.
The resistor in the circuit "persuades" the power from the key to go through right relay instead of doing into the radio. Also give the radio more juice, limiting flow throught right relay.

Doesn't this require relays that are capable of turning on with only 6 volts since relay control circuits are wired in series?

 

[luv2rallye]

Doesn't this require relays that are capable of turning on with only 6 volts since relay control circuits are wired in series?

Ya and that's not the only problem...I don't even want to get started.
VR4 Kev: You've got the best and workable design - see my post 22.

 

[VR4 Kev]

luv2rallye, I am using the 3rd relay to isolate radio power when you key off so this circuit doesn't back-feed your key-switch and keep other items alive in the vehicle.


Fixed labels.

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[luv2rallye]

luv2rallye, I am using the 3rd relay to isolate radio power when you key off so this circuit doesn't back-feed your key-switch and keep other items alive in the vehicle.

Ah... VERY GOOD CATCH!
Operating the door switch would also do that but until someone does, power would be backfeeding even though the key had been turned off! Not a good senerio.
I'm giving you rep points for that well thought out detail that most would miss!
Good job on both the circuit and the catch!

 

[echamp_1]

It doesn't seem all that work is worth it just have your radio stay on with the key out. Newer cars, as stated before, use a body control module to do this. They have a RAP relay (retained accessory power) or sometimes a separate module which works off a timer of usually 10 minutes or so. I learned this stuff in school last year when I was in electricity class but I don't remember all of it . Basically when you pull the key out of the ignition as long as you have the driver side door shut the timer count down will start. During that time you should be able to use power windows, radio, etc. If you open the door the accessories stop because it assumes the driver is leaving the vehicle. I'm sure the above diagrams would work, but I don't see it being worth it in the end. All the modern day electronic stuff is nice but can make cars a lot more complicated to perform repairs on when you get those electrical gremlins. I prefer a car that is easier to work on .

 

[luv2rallye]

It doesn't seem all that work is worth it just have your radio stay on with the key out. Newer cars, as stated before, use a body control module to do this.

Well I agree with you but that's not the issue. He wants to do it on his present car and is asking for advice on how it can be done on his present car.

 

[luv2rallye]

VR4 Kev: Although your circuit in post 28 works I just realized it has a safety issue. When key is on and door not open, the "+12v" is connected to the "key +12v" through the left 2 relays. The normal ignition key on position (which is your "key +12v") supplys up to 30A (through 30A "IGN SW" fuse) to run all kinds of stuff. But now it can backfeed that power through your "+12V" line and those relays.

The problems are:
1) You would have to run 12 ga wire (like "IGN SW" fuse uses) for all these backfeed current carrying wires in your circuit - which is not practical or desirable.
2) You are now bypassing the 30A "IGN SW" fuse for that power which is not desirable. Think of the troubleshooting nightmare when the 30A fuse blows (or is removed) and things are still on.
3) You would need a 30A fuse in the "+12V" wire (to protect wires in case of a backfeed current short).
4) You now have to use 30A relays.
5) Those circuits are getting power from 2 sources which is never desirable. In fact some of them you want to turn off when key is turned off.

Here's a possible solution:
Replace the relay on the right with a diode (forward biased - arrow pointing down) that can handle the radio current (current for case of both key on and door open). That will prevent any backfeed.
[Of course there's a time you'll get a 0.7v drop across the diode but that will only be for 1) the instant until the left relay latches up, or 2) for the case of both key on and door open which is rare case. And even then a 0.7v drop is not going to keep the radio from working.]