Battery? Ignition Switch? Earths? All of the above?????

I swapped out the starter on my 89 200TD 90 recently and all was going swimmingly.
When I did so, I also put on a new battery. The last few times I've started her up, it was turning over slower.
Went out on Saturday and it wouldn't turn.
A few clicks but nothing.
I fully charged the battery and all I get now is the dash lights coming on, until I turn the key to start and it all goes off.

I checked for current drains but found nothing.

I am going to return the battery to make sure it wasn't a dodgy one.

Any other suggestions??

I want to get it sorted as I'm meant to be camping this weekend!

Worth checking out the alternator also. Pending on the age they can fail too. If okay sounds like it's not charging or a wire failed.

It does sound battery failure, rare but it can happen.
Are you able to jump start the car ?

With the engine running you should be able to check the voltage across the battery and see if the alternator is charging.

I got the battery checked and it is A-OK
I’ve picked up a brand new ignition barrel and I’m thinking that’s where the issue is.
Need to get it swapped out one evening this week as I’m hoping to use the tent on Saturday evening.

have you checked your connections are right on the starter motor as it seems to have stemmed from that point

I am with mystery on this on, more likely a heavy cable connection problem.
The clicks you hear tell you the ignition switch itself is working sending power to the solenoid starter [thing that is clicking]
Make sure you have a good earth from bolt on gearbox to the battery. If not good the current try's to return to the batt other ways like down hand brake cable, speedometer cable and melt them.