delay relay on time

I'd like to power the coil of a standard Bosch 30-amp automotive relay through a "fading" power source.  From what I've read, using a fading power source will cause "chattering", which is something I'd like to avoid.  Is there a way to wire the coil so that the application of voltage to coil contacts will be delayed until the fading power feed reaches atleast 6 volts?  Also, is there a way to wire the coil contacts so that the coil immediately de-energizes once the voltage reaches 6 volts as the power feed fades out to 0+vdc?

The relay should not have a problem with the increase from 0 to 12, I think it takes more than 6 volts to energize the relay.  I do not think there will be any chattering in that phase of the process.  The chatter experienced upon the diminishing voltage is usually cured by a capacitor and a diode.  But before we try that, I need to know what kind of current the device is capable of.  I do not want to help you burn it up if it can not charge  a 1000 mic cap along with the devices it powers.

After re-reading your post, the above will only eliminate the chatter.  It will pull in when it pulls in.  That will be whenever it reaches the 7 volts you referred to earlier.  If it is taking longer than you like turning off, you may try a 470 mic cap.  

I don't think you need to worry about the chattering of the relay; that'd only tend to be a problem if your battery is being affected by the load, such that the voltage jumps up when the relay disengages, and goes up enough to engage the relay again. 

Relays have a certain amount of built in hysteresis that you shouldn't have a problem with this unless your battery is really weak.

More of a concern is that it sounds like you're driving fairly heavy loads, and switching relays slowly tends to be hard on the relay contacts, because the resistance goes up as you approach the point where it's at the turn on or turn off threshold.   It could possibly overheat the contacts and cause them to fail earlier than they normally would if you drive them fast and hard.

If you can use another control like Howie suggests it'd be better-  otherwise you could add a solid state relay driver, though it'd probably be more trouble than you want to bother with.  Or just try it as is; it should still last a while even with the slow switching, and it doesn't sound like it's a critical kind of function, being just headlights.

deja vu