head unit survivng crank

**04scooby** · 10-20-2005, 11:05 PM

now that I have my yellow top battery my car PC survives crank but my head unit still "reboots". How can I do this?

Thanks

**Cris** · 10-21-2005, 06:49 AM

This happens on almost all the new cars...I don't know if there's any way around it, except maybe running a separate wire from the battery, but I can't say for sure that would help.
I too am interested in this...

**Enforcer** · 10-21-2005, 07:15 AM

Originally Posted by 04scooby

now that I have my yellow top battery my car PC survives crank but my head unit still "reboots". How can I do this?

Thanks

the headunit has two positive leads in, one is connected to permanent 12V the other off the ACC 12V. The ACC 12V has power disconnected during a crank.

The constant 12V on the HU is to keep the settings stored in memory.

The ACC 12V on the radio tells the radio whether to be on or off.

Therefore no power on the ACC12V input means HU is off.

Now you could wire the ACC 12V of the HU to a constant 12V but you would then need to manually turn the HU off/on each time you get into the car, otherwise you would end up with a flat battery.

**04scooby** · 10-21-2005, 04:09 PM

I was wondering if maybe putting a relay of some sorts on the acc, so when it is activated it will complete the circuit on the head unit power from the battery.

Would this work? If so what kind of relay would work?

**turbocad6** · 10-21-2005, 04:35 PM

that will work fine, BUT you must use a diode so the temp jump don't backfeed the rest of the accessories in the car!!!!!!!!!!!!

use a regular 5 term standard automotive relay.... bosche, potter brumfield, etc...

diode is a must though

basicly you'll have the ign feed the radio with the accessory wire at the same time....a diode will make sure that the whole ign isn't feed when your key is back to accessory... you really could do this with just a diode & no relay even come to think of it... real simple..... just jump a ign to the accessory wire at the radio, with a diode in line with the ign so it's not backfed.... problem solved

**gt__1** · 10-21-2005, 04:54 PM

do you have an opus or carnetix then just wire it to that. wire it in parallal with your cpu and it should work fine

**gommino** · 10-21-2005, 05:02 PM

Originally Posted by 04scooby

I was wondering if maybe putting a relay of some sorts on the acc, so when it is activated it will complete the circuit on the head unit power from the battery.

Would this work? If so what kind of relay would work?

Do you mean between the battery and the acc line that goes into the headunit? If so, what's the point? You would then have to activate the relay and then switch on the headunit. Just connect the line to the same line that has the constant 12v and use the headunits built-in on/off switch.

The picture below is from the installatin manual for my headunit. Use the layout in section 'C'. The left hand side of the wires is the headunit and the right hand side is the car.

Rob.

**04scooby** · 10-21-2005, 06:36 PM

I mean running a constant 12v line and tie the relay into the acc. Since the realy is installed inline to the constant 12v, it closes the circuit on the 12V and the radio turns on. When key is moved to off the relay closes and radio powers off. I have a KPI 250W PSU so I cant tie into that.

**turbocad6** · 10-21-2005, 06:45 PM

there are four distinct circuits at the ign switch..... 1 is constant power always, 2 is ignition that has power with ign on & through crank, but not in accessory pos.... the 3rd is accessory which has power with ignition on AND when the key is in accessory pos., but drops power when vehicle is cranked..... this is to unpower any accessories to allow more cranking amperage available.... the 4th isn't a concern here, but is the actual crank signal

your radio is on the accessory circuit, that's why it works when the key is turned back & when the ign is on, but dies on crank.

if you switch the radio from accessory to ign it won't die on crank, but it also won't come on when the ign is turned to accessory

to have the radio work from accessory thru crank you will need to feed it power from both circuits..... not a problem unless in doing so you cause the accessory to feed the ign or vice versa

a simple diode will allow you to power the radio from both circuits without having one affect the other anywhere else but at the radio........

**turbocad6** · 10-21-2005, 06:52 PM

sometimes these circuits are multiples, & that's why there are more than four actual wires at the ign switch, there can be two or even three constant feeds & there can be more than one ign or accessory, but still 4 distinct circuits

the only other wire at the ign switch will be small gauge key sense circuit or sometimes vats security or something similar