automatic turn off delay

I did Search, and while my quandry may have been answered somewhere else, I didn't recognize it or understand it.

I have a custom car build with From-Scratch wiring. The car originally had a Rear Window Defogger that shut OFF after X minutes. I want to create the same thing. It still has the OE Defrost lines in the glass, and I'd like them functional. There is Absolutely ZERO original wiring.

Could someone please explain in SIMPLE terms, how I wire the circuit, using a push button switch, to turn itself off after say, 10 minutes ? What components do I need specifically ? PLEASE

Thanks for looking ...

Search for 555 timer circuits that drive a relay - eg circuitdiagram.org - time delay relay. Note that the relay coil has to be less than about 180 Ohms. Some circuits add a diode between pin 3 & the relay - line towards relay (86).
The 1M can be changed to a pot or trim pot (variable resistor) to adjust the time.
As per the text, the resistor and LED are optional.
Usually a 10uF and 0.1uF cap between + & gnd (ie, between pin 8 (or 4) and pin 1) would be added to prevent spurious triggering, but for a simple on-off delay the can be omitted - it's only in astable mode (cyclic switching) that that's required.


Or get a DEI 528T (timer relay).

Get a GM rear defog relay / timer from a 80's-mid 90's era GM. Does exactly what you want, in a compact, inexpensive, self-contained unit. In this pic, the relay is in the upper left, the dash mounted switch in the lower right. This set-up looks like its from an F-car.

I found one of these Defogger relays in my stash. GM P/N 15554520. I found several available online. I took it to the bench and got it to work. Here's what I found. They have 5 terminals that are labeled on the relay:

L = Output
B = B+ Hot at all times
G = Ground (-)
I = Ignition. Must be +12V for relay to energize, if removed, relay turns off.
P = Control. (+) pulse turns on, (-) pulse turns off.

Note: Relay times-off after appx 10 minutes. If pulsed back ON during same ignition cycle, next timed interval is appx 5 minutes.

THANKS SO MUCH GANG !!!

I'll look for that GM part number right away !