There are two connectors with nothing connected to them:
One on the left side under the saddle with four male pins in a grey housing with a black cover
The other is a single female connector on a red cable in the middle of the saddle front end.
My bike is a 2006 Heritage Soft tail classic.
Anybody knows what are they for?
Thanks

 

I don't remember which one, but one of them is for the shop to plug in and diagnose

 

The gray one with the black plug.

 

Welcome to the forum from Texas.

As stated, the connector with the four pins, grey housing and black cover is the diagnostic port.

Since it is a used bike, the female connector on the red wire can be anything. Test it with a digital voltmeter to see if it is a usable wire you can tap into at a later date. Is it connected directly to the battery as a 12v hot lead all the time or is it a 12v lead connected to the accessory circuit? Maybe it's a dead lead that was once used for something and can be removed.

 

The gray connector at the front is the Batt+ accessory plug, many accessories for your year plug into it, you can also buy a harness adapter from the P&A catalog to hook anything you want that needs 12volts keyed power to it. As other have said the 4 wire gray plug is the data link!