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Hooking up Relay and Switch



Jan 1, 1970
I am going to do some work in my car. So everything I talk about
should be ~12 volts. I have some electronics knowledge, but I am no
expert. I plan to use a relay to switch certain things. Here is how I
plan to hook up the relay (coil side):

Battery positive to toggle switch
Toggle switch to relay coil
Relay coil to ground
Ground to battery negative (Of course)

This will not be a short, will it? (Or do I need some sort of resistor
in there?) The relays I plan to use can be seen at
The important detail (I think) of the relay is that the coil is 72

Also, is it safe to use DIP switches? I don't know if they can handle
the current that will go through the relay coil.


Jan 1, 1970
Andy, don't forget to fuse both your switch and your supply leads. I
have been in the auto electronics biz for almost 20 yrs and have seen
many cars that got burnt because of careless (unfused) wiring. Good

Si Ballenger

Jan 1, 1970
I can't speak for today's cars, but in years past the coil was
designed to run on ~9v instead of 12v. The reason for this was
during cranking the system voltage would drop to around ~9v due
to the very heavy starter pull on the battery. In the start
position the battery was fed straight to the coil. When the key
is released back to the run position, the battery was routed
through a ballast resistor to drop the now system 12v down to the
9v for the coil.