Hey guys. In the past year i have fitted a full NF dash, loom, heaterbox ect.. into my EB V8. Just the other night i noticed that when my heater is on the thermos come on and cool the engine to way below where it should be?

Has this ever happened to anyone before?

Just to throw a spanner in the works, all the parts i used come from different cars but i had both wiring diagrams and made sure everything would be where it should.
Here is a list of the parts i used.

EL V8 opt20; ecu, engine bay loom.
NF I6 GHIA; body loom, bem, climate control.

any ideas?

any help appreciated!