So what are the specs for the diode for the #21 and +12v for the IAB... Can any diode work, I put a 3amp diode in there... I want to make sure it's safe before putting the harness back in...
Use a 1N4003, available at Radio Shack, stock number 276-1102. the 1N4003 is rated at 200PIV, 1 amp, which should be fine for a surge supressor. Remember the band on the diode goes towards the + wire when you use it as a surge supressor. This is backwards from normal use. Put it in wrong and you will make probably make smoke.
A diode used as a surge supressor does not carry much current, but it does need a fairly high breakdown voltage.