Returns

[rumrog1]

I want to return a non working item. But can not do so as it is a car stereo with a dashboard replacement until I have a new one. My vehicle would be illegal to drive with this missing. Seller does not acknowledge this 

[tressygirl]

It' not the seller but eBay rules, that is,  and item that has to be returned needs to be done within 30 days of delivery.

If this includes the timeframe for you keeping the vehicle all good, otherwise your will be out of time to claim from eBay.

[red_magpie]

Seller does not acknowledge this

Neither would eBay. You know the rules: to receive a refund or replacement you first have to open a case and return the non-working item. 

If you can't use the car without it you may need to take the car off the road until it's resolved. Or to buy and fit a replacement from another seller (or even from the same seller, if you want) while waiting for a refund from the original sale.

[arkwebus]

This is - perhaps - one of the disadvantages of buying on eBay.  If it really "illegal" to drive without a stereo then your options are as set out by @red_magpie .

As long as you are within the 30 days from purchase it's very likely under eBay rules that you will get a full refund of what you paid but - sadly - what you will not get through eBay is any form of compensation for time off road/fitting. 

You do not need any communication with the seller [it only wastes time and may run you out of time].  If you miss the deadline eBay will not help

@rumrog1