the 7805 has output over load protection (you can short it to ground) and has over heated protection, it shuts down, cools down and then wakes up when cool enough , but... a) Applying too high an input voltage. Do not, under any circumstances, apply an input voltage higher than the absolute maximum, Look at the Recommended Operating conditions for the maximum steady-state input voltage that can be applied. Since a Vehicle can have spikes on the 12V electrical system, the 7805 should be protected at a minimum, with a good-sized input cap of around 10uF, 25V. electrolytic will do, but tantalum is much better, and multi-layer-ceramic even better yet. You do not always need an output cap, but if you use one, it should be smaller than the input cap, say 1uF or so. One of the worst killers of 7805's is the use of a large (or even a medium-sized) output cap, and then have the 7805 input to ground pin get shorted or quickly discharged. This will force the 7805 to discharge the output cap thru the 7805, which likely will damage it, if it is a big enough value. There is a simple fix for this, which is to install a diode (1N4004 type or similar) with the anode to the 7805's output pin and the cathode to the 7805's input pin. This will force any discharge thru the diode and around the 7805, protecting it. This is only needed if you have the potential for a quick discharge of the 12v input to the 7805. The 7805 is nearly indestructable if you watchout for the 2 pitfalls I mentioned. In a car, just the A/C compressor, clutch alone can creat a huge 400vdc spike at is releases, over and over (A/C logic ) or jump starting a car. Any load dump, condition can to that. Inductors have huge back EMF spikes. The Car battery shunts many spikes but as you know, they can be old batteries, or with poor connections.(reality) Some newer cars and for sure the TCC solenoid have internal snubbers that stop EMF back kicks, but most coils don't in older cars. the Design you make , should be for older cars. if building 5vdc logic that needs more power and you hate large heat sinks they this out. (it's a switcher !) http://www.murata-ps.com/data/power/oki-78sr.pdf