Constant Input to Momentary Output

Hello, I need to convert a constant 12v or ground input to a 30-60 second momentary 12v or ground output. It can be up to about 5 min. I am doing an engine swap in a jeep and this is for the fwd actuator solenoids, They are not 100% duty cycle. I looked around and i can't seem to find anything, If everything fails, I will use an arduino but i rather keep it simple with a few transistors and caps. Fyi, the two vacuum solenoids draw 0.5A at 12v each, the relays that can be used draw about 0.136A at 12v ThanksI own and operate Derks Custom Cars, Mostly doing LS engine swaps while retaining full vehicle functionality, Incl gauges, ABS, etc

I'm trying to understand (grasp the concept of) what you want to do. If you were to convert a constant to a timed output, it would give you a timed output, but only once. Would this be ignition power instead, perhaps? That way when you cycle the key you'd get your timed output again?My ex once told me I have a perfect face for radio.

yes only once is fineI own and operate Derks Custom Cars, Mostly doing LS engine swaps while retaining full vehicle functionality, Incl gauges, ABS, etc

Do you mean once per ignition cycle, or just once, ever, until your battery dies or is disconnected? I'm still trying to figure out what you mean.My ex once told me I have a perfect face for radio.

The two solenoids are controlled by a regular bosch relay that is energized when the transfercase is in 4x4. for the front axle to engage or disengage a short, about 5 sec, is needed to shift it. so one vacuum solenoid to engage, one to disengage. they can not be energized for more than about 30 min as they are heating up. (if they where continues duty, i wouldn't have this problem) Originally the front axle actuator was controlled by a vacuum switch on the transfercase. 12v ign on 30, engage on 87, disengage on 87a. the transfercase switch controls the relay. that relay can control the solenoids directly if i can put the timer between the relay and the solenoids. Thanks I own and operate Derks Custom Cars, Mostly doing LS engine swaps while retaining full vehicle functionality, Incl gauges, ABS, etc

Okay, I think I understand now. While there are many ways to achieve what you want, I think I'd use a couple delay off relays controlled by a couple more automotive relays (total of 5 relays- 3 automotive(Bosch)/2 delay off). Terminals 87 (engage) and 87a (disengage) of your first relay will feed the coils of relays 2 and 3 using the constant to momentary output diagram: https://www.the12volt.com/relays/relaydiagram20.html The outputs of relays 2 and 3 will feed your adjustable delay off relays (check Amazon, eBay, etc.). Alternatively, if you want a standard automotive relay configuration, look at these: https://www.altecautomotive.co.uk/timer-relay-fully-adjustable-12-volt--------braltt40205-09-1614-p.asp *Note these ship from the UK, so they may take a while to arrive.*My ex once told me I have a perfect face for radio.