Would it be possible so that the radio has constant power from start to run? That way the radio doesn't have to turn back on all the way if your just listening with the key in start, my new radio takes like 45 seconds to start up.

 

you always have a small amount of power going to it already...in order to keep the clock and keep the radio presets and such things like that. Just a thought.

 

Ya but I want it so that it doesnt lose power when the starter cranks.

 

Don't quote me on this but I think thats because the starter draws so much current.

Maybe if you had a big enough cap in there, and wired your radio to it (but then it would always get power)...

I'm not real sure on this.

(EDIT: I think I'm wrong)

 

No matter what you do your starter will always draw a shiz load of power. When i was really into audio systems i did this and wired up a switch so i could shut it off and stuff since i never used my clock or listened to the radio. I had a 6 farad cap on there powering everything and even when i started my truck the cap lost power and the radio still shut off for a few seconds there is no way around it your just gonna have to deal with it unless you run the radio on a separate battery from the starter but then you gotta worry about wiring it up so that at the flip of a switch you could have that second battery jump on your circuit to charge up. If you really wanted to do that i would do the latter but thats a lot of wiring. lol /end soap box

 

There has to be a way to rewire it to work, maybe some relay setup. I'm waiting for Bob to chime in.

 

Give this a try Trent. I can't find the switching time on these relays, but the headunit internal decoupling capacitors maybe enough to maintain 12V on the "SWITCHED 12V" while the relay is switched from the N/C to N/O positions and back.

 

The voltage drop during engine crank will likely cause it to shut off even if it was connected to a constant source of power.

 

I don't think so, the "UNSWITCHED 12V" sees the same voltage drop. However, if the battery is on it's last leg, this might be another story.

 

You did remind me of a "feature" on Saabs though. They have a "negative peak detector" that stores how low the battery voltage goes during cranking, so you can tell when your battery is starting to fail.

 

There is also a "make before break" SPDT relay, if the switching time is too long on the standard automotive SPDT relay.

 

Starter draw should not turn the radio off if it is wired up another way. Ford has it turn off all accessories so that if you have a low battery it will help get more current to the starter. Radios take very little current to stay running.

If you were to find a wire that is hot while cranking, or use a simple toggle switch, you will be able to do it.

 

Unfortunately the circuits that are hot while cranking are "UNSWITCHED 12V" circuits, and he would risk having a dead battery....

 

So like the fuel pump that is on while running and cranking wouldn't work eh? As a input for a relay.

(not 100% sure our trucks pump runs while cranking, but i believe it does.)

 

Sorry, the PCM determines when the fuel pump runs, by picking the relay.
Matter of fact, if you turn the ignition to the "RUN" position (without starting), the fuel pump will run for a few seconds, then shut off.

The "start 12V" should work just fine in the circuit I posted.

 

However, The 12V feeding the fuel pump relay is HOT in "run" or "start" so that would work great!!

You can pick this up off of fuse #13


Good going Mike!!!

 

Trent, when you play your radio without the engine running, do you do this with the ignition switch in the "RUN" position, or "ACCESSORY" position? If you use the "RUN" position, then the switched 12V circuit going to the fuel pump relay will work. If you use the "ACCESSORY" position, this circuit will not work.

 

I use both, I can use Acc if thats what keeps it working. I'll try it using the fuel pump relay today!

 

I have this done for my AVIC to speed up loading time, also using the fuel pump circuit for a trigger, works great!

 

I had it wired up in my Jeep so it would do this.

If you wire it wrong (like I did), you will also have to turn it on and turn it off manually rather then it coming on by itself. The above diagram is how I did mine too.

 

Just remember if you tie the head unit's "switched 12V" to the 12V going to the fuel pump relay, ACC will not work. If you use the relay circuit I posted, ACC will work, and going from RUN to START won't shut the head unit down.

 

Awesome!

 

So i would use the fuel pump relay to pin 86 or pin 87?

 

If you use the 12V going to the fuel pump, you won't use the relay. Just tie the head unit's "switched 12V" to the 12V GOING to the fuel pump relay. Make sure you get the 12V GOING to the fuel pump relay, not the 12V coming from the fuel pump relay going to the inertia switch. But, remember
ACC will no longer work. Using the 12V going to the fuel pump relay will keep your headunit from powering down when you go from RUN to START.

 

Ok I'll do that first then, it sounds easier for now. Its not really an issue if acc works or not. Thanks a lot!