... check the connection at the yellow crank/starter wire.
The starter circuit is wired in series through the rs system. The starter wire is cut in half with the grn wire from the alarm going to the key side and the purple wire going to the starter side. If it was a bad connection, the truck would have problems starting with the key also.
did you install this alarm? it sounds like it is set up with out the tack wire... do you have the neutral safety switch on?..
An open circuit signal from the tach and neutral safety wires won't keep just the starter circuit from activating. These wires will keep all the RS circuits from powering up, including acc and ign circuits, not just the starter circuit.
On the 5701 unit, the only time all other circuits activate w/o the starter activating is when the rs override switch is off. This is a new feature on the 5701. Unlike previous models, the toggle plugs into the unit rather than splicing to the blk/wht neutral safety switch wire and ground. So now you have a neutral safety switch wire that needs to see ground and a seperate safety shutdown toggle switch. Make sure this switch is in the ON position. Depending on where it's installed, you might have accidentally been kicking it on/off w/o realizing it.