Need Help Wiring a load Fault Indicator

You're welcome, Trent.

CBB

CBB/Trent:

Select a TVS and 1n5403 or 1n5404 for Trent and update the schematic.

I'd recommend one of these: https://www.digikey.com/product-search/en?vendor=0&keywords=P6KE22A-E3/54GICT-ND
18.8 and a 1n5403 diode: https://www.digikey.com/product-search/en?vendor=0&keywords=1n5403

Both of these would be mounted close to the power in to the circuit.
Both diodes would be placed in the schematic with the band toward +12 and the other end to ground.

The idea is to suppress spikes > -0.6V and > 18.8 V. The Peak reverse voltage of the 1n540x diode has to be above 200 V.

This isn't the BEST protection, but it's better than nothing at all. Linear Technology does make an IC that is designed to implement a surge protected 5V supply for automotive use. The automobile electrical environment is extremely nasty.