528t pulse timer

Hello, new guy here.  I am accessing this forum to hopefully find guidance regarding the installation of a 528T pulse timer.  I do installations of alternative fuel systems on diesel vehicles & equipment and have run into a snag.  On my current project, I decided to simplify the controls for switching from one fuel type to another by utilizing the existing rocker switch on dash (for switching between front and rear fuel tanks).  The rear tank holds conventional diesel and the front tank (I will refer to as the auxillary tank) used for bio-fuel.

When running on bio-fuel (straight vegetable oil) the vehicle's fuel system must be "purged" for about 60 seconds before parking for an extended time (overnight etc).  There are two 3-way solenoid valves under the hood.  Valve #1 switches between the two fuel tanks using the stock rocker switch on the dashboard.  Valve #2 is used to swap the fuel return.  When switching to diesel, if valve #2 was allowed to switch from returning fuel to the aux tank to returning fuel to the diesel tank, the small amount of residual vegetable oil in the fuel lines will be returned to the diesel tank which is not good so I need to delay valve #2 for 60 seconds to accomplish a "purge cycle".  The valves are wired to switch to veg oil upon receiving a 12V positive charge and will default to diesel when power is removed.  I purchased a 528T programmable relay to do the "delay" job but didn't understand until now that it is triggered by a pulse, (either neg or pos) not a constant, to start the 60 sec delay.  I initally thought that I could wire the trigger to the constant 12V and have it trigger when the 12V was removed but now understand that it requires a single pulse, either + or - .

Could anyone advise me on how to create a single "pulse" when the 12V is removed.  I hope this all makes sense...I am not very knowlegable on electrical issues & sorry for the long post.

Thanks in advance....

If you look in the relay diagram section there are a few options for you. Based on your post you are looking to convert a constant +12V to a pulsed +12V right? Constant to Pulsed (+12v) If you want to "block" the valve for 60s by using the timer, then you can use the timer in addition to a relay wired to invert the logic. Wire the relay for Normally Closed (87a and 30) so that when the timer is active, it will open the relay during the 60s blocking time.

What I am needing is a single pulse, either + or - to trigger the timed relay when the power is turned off to the aux fuel system.  The vehicle must be started on petro-diesel and shut down on same.  When engine is warm and system is manually energized, the solenoid valves align for aux fuel.  When power is secured (i.e, the rocker switch on dashboard is set to the rear or diesel fuel tank), the valves default to conventional diesel fuel and the fuel returns (from valve #2) are aligned to return the fuel to the diesel tank.  The problem is, there is a small amount of veg fuel in the lines that will return to the diesel tank (not good).  A 60 sec. delay to valve #2 will allow the residual veg fuel to return to the veg tank which purges out the fuel lines so the engine will be ready to restart on diesel fuel.

Please forgive my lack of knowledge regarding electronics but it looks to me like the diagram shows a situation where a pulse is generated upon the relay receiving a positive signal.  I need a single pulse generated when the power is removed.  I know I can achieve this with a momentary contact button on the dash board but I'd prefer that it happens automatically when switching fuels using the stock switch on dash..

Thanks for your reply.