I have a 67 mailbu and just bougt a replacement horn relay from year one. The new relay has and extra terminal that my original did not. There is the two terminals under the divided plastic housing abeled 1 and 2. The two connected terminals on the front of the relay for the hotslabeled 3 and 5, and another single terminal in the back labeled 4. My original does not have terminal 4. What is this for and how do I make it work?

this is for a key buzzer that the 67 does not have. will work just fine.

thanks alot for the response. you guys have all the answers