206 HDI LX car stereo

Hello im andrea and ive just got my 1st peugeot about a week ago. The radiowas well naff and ive got my fella to change it. the speakers were shot. We got a pair of speakers from a bubble shape nissan micra from the front doors, which were an exact swap and now has nissan blaupunkt ones and sounds cool at just £10.00 from my local scrap yard. The dodgy cntral locking is now fixed. Just one thing to do, which my man is baffled by.

There is a red light on the dashboard that keeps coming on. something to do with the coolant, but its full. Any ideas what the issue may be?

I'd be really greatful for any suggestions.

Thanks

Andrea xx