How to fix rear trunk speakers?

I have a 2008 Ford FUSION SE. I've bought 2 6x9 speakers to put on the back trunk deck because old ones didn't work. So I've installed them and used the wire harness to make it easy to install. But they still don't work please help. Also yes I've installed speakers b4 on this car. I've put 2 6x8 kicker speakers in my doors

Your speakers didn't work because you aren't getting a signal from the unit… Duh!

Hi so you need an auto electrician

Is the radio factory or after-market?

The rear 6x9" speakers in a Fusion are bass speakers, driven by a separate factory amplifier. If you've replace the head unit, you have to use a special harness and do a bit of extra wiring to make the bass amplifier work. If it's still a factory radio, there may be a problem with the factory amp. Either way, you won't get sound from them unless the amp is working to drive them (and when you do get sound, it will just be bass, not full-range).

Try adjusting the fader on the radio. If that doesn't fix it the rear output of the stereo is blown out, or shorted. You need to test the speakers on a known sound source to see if they actually are the problem. So, now, you have two sets of speakers not working on the rear channels of your radio. Something is probably wrong with the rear channels of the radio.

"Rear trunk speakers" is a bit redundant. How many cars on the road today have a front trunk besides the VW Beetle?

Gotcha.

Look in the stereo menu. If it is a 4 channel (or greater) head unit there's probably a setup sub-menu that controls rear speaker and subwoofer function and you have to select the setup you are using. Eiother that or you are using the incorrect adapter harness.

You're going to need a separate amplifier to drive those speakers so they get the proper power they need if you've already got 4 speakers running of off your headunit.

"The old ones didn't work" should be your clue, there's probably a factory amplifier module for the rear deck speakers.
The rear deck speakers are taped off the rear seat door speakers and only work with the factory upgraded Sony unit.
To make them work will require a 2 channel amplifier with high level inputs fed from the rear door speaker wiring. The factory Sony upgrade unit has a 6" round duel coil sub with 2 6x9 coaxial drivers and a factory internally crossover network high level input amplifier module in the trunk to drive the rear deck speaker array.

Now assuming you do have the factory amplifier (I read your comments on replacing the deck), you will need to reconnect the proper amp trigger wire from the old head end deck vehicle harness connector to the new stereo power antenna / amp trigger wire to turn the factory installed amplifier on, just like the blue wire on aftermarket audio amplifiers.