Car was nto charging and no dash lights worked, about a week ago replaced voltage regulator and all electrics came back to life and salternator started charging battery. Drove for a week and suddenly dash lights died again and is no longer charging. Is it likely to be a bad replacement regulator or more likely another problem? Battery is new.

 

It would be helpful to know if you are n the USA.
Do you have a Digital Volt/Ohm Meter?

With the Battery Charged up when you first turn the Key on do all of the Dash Lights light up including the Battery Charging Lignt?
If all work but the Battery Charging Light does not come on it could be that the Bulb in the Battery Charging Light is no good. Your system needs to have this Light Bulb working or you Alternator will not charge.

Also before all the Dash Lignts went out was the Battery Charging Light on? If it was on your Alternator was not charging.

The other stuff you will need a Volt meter to check.

If you are in the USA you Can get someone to jump start your Car and drive it to an Auto Parts store and have them do a free electrical test.

Besure that your Alternator Fan/Drive Belts are tight enough and are not covered with Oil.