Hoople
Account Removed
It really should say it on the package. It is a negative for the manufacture to build the relay with an internal diode. Once the relay has this diode, it now has polarity that must be followed. Having a diode now limits the ways it can be hooked up. So the internal diode stops the relay from being "universal" and limits it uses for the "experimenter".
You can use a Fluke meter and get an idea of what is inside. But it's best to see it on the package.
You can use a Fluke meter and get an idea of what is inside. But it's best to see it on the package.