My Dodge Cummins truck has an exhaust brake and it uses a signal from the ECM to activate the vacuum relay to engage the brake. I would like to make it a little smarter by having it automatically disengage below 15 MPH. I can get the signal from the VSS (Vehicle Speed Sensor) that is used for the ABS system. I can then process this signal to give me an enable or disable signal in relation to vehicle speed. I'm thinking of using a 555 and using the VSS signal to reset the timer if it's fast enough. Any ideas on other ways I might accomplish this?