Cold engine light won't go out

Ok so I have a 1995 defender 90 300tdi.. My first defender in very good condition, only done 75000k. Just had the alternator totally refurbished and battery fully charged up . Now the cold engine light won't go out! Checked everything obvious, all seems fine. Suggestions welcomed on what could be the problem.

By "cold engine light "do you mean the heater plug lamp?

It's the light underneath the diff lock light. It's called the cold start light in handbook. Does that help?