I recently added a magnetic switch to my tailgate and connected it to my factory alarm. Now the alarm (and train horn) will go off if anyone opens the tailgate when the alarm is armed. Cost was less than $10 and it works like a champ.
I had to use a 12V DC relay to connect the normally closed magnetic tailgate switch to the normally open factory hood switch circuit:
The relay is tiny and it stays powered 24x7. I am not worried about battery drain since the relay coil only draws 37 ma of current. My concern is that the coil may eventually burn out or wear out since it will be powered 99% of the time except for when my tailgate is open.
Has anyone else installed a small relay for their train horn or a similar automotive system where the relay coil is charged most of the time? I would hate for the coil to fail late one night while I am sleeping. The truck is parked close to my bedroom window so it would give me a heart attack if it lets loose in the middle of the night. I checked the technical specs for the relay but it doesn’t mention anything about maximum coil charge times or longevity. It does say that the relay is designed to handle 10,000,000 manual cycles but I won’t be opening my tailgate that often so this stat is moot.
I know I could just use a normally open magnetic switch and eliminate the relay but this is a bad design for security systems. Someone could cut the wire or remove the sensor, or a wire could come loose or a fuse could blow and your alarm would never be tripped. The factory alarm only uses a normally open switch on the hood because the hood switch wiring is protected by the locked hood and the factory wire is run inside of steel channels around the engine compartment.
Any thoughts from the wiring gurus out there?