A hood-pin is a switch which indicates whether the hood of a vehicle is open or closed.

Some brands of car alarms and/or remote starters (Autostart, Astrostart etc.) require a working hood-pin in order to access key fob programming and/or feature programming.

Please see the image below for what an after-market hood-pin commonly looks like:

A hood pin is a common plunger style pin switch that switches a chassis ground (-) output when the plunger is in the up (electrically closed/hood open) position. The chassis ground (-) output goes away when the plunger is in the down (electrically open/hood closed) position.

Hood pins are prone to many problems, mostly tied back to the environment they are installed in (under the hood near the hot engine, exposed to water, dirt, road salt, and other contaminants). Hood pins are also prone to breakage, especially by mechanics who slam the hood down on them, leading them to bend and break.

Rust and dirt are the other leading causes of non working hood pins. Always inspect the hood pin, if you see rust or dirt on the electrode (the spot where the wire plugs into the pin) then it is more than likely not working, The rust and dirt need to be cleaned off, or the hood pin needs to be replaced.