Perplexing relay application

Hello guys, Im new here so be gentle! I am glad to find a place to exchange ideas.

Ok, I have a weird install question here, I had a customer bring in a RV, he has a 110v amplifer that he wants to use in the back of his RV to run some outdoor speakers but he wants to use his 12 volt head unit as a source, no problem there. But I need a way to turn this amp on via the 12volt turn on lead from the head unit. The amp has a input in the back for a remote momentary power switch that is rated at 12 volts. but no normal trigger input.

My question is how can I take the 12volt  constant and make it pulse a momentary on, and when the head unit is turned of, it repeats the process again to turn the amp off. I understand how to use a relay to make a constant signal into a pulse, but how would I also reverse the process?

Thanks in advance,

Allen 

Help me understand.

I think you want a positive pulse to turn the Amp on and then a positive pulse to turn it off.

When the remote from the car radio is on you want a positive pulse.

then when you turn it off you want another positive pulse. Right?