2000 Ford Mustang not showing total mileage?

I just added some new lights to my 2000 v6 mustang gauge box, but then when I try to start the car again it won't even start. Like you turn the key and all you hear is the starter but its not going past that. What is wrong? Before I replaced the lights the car was running perfectly but now when I turn it on it has the "Service Engine Soon" light come on. Does anyone know what I should do/check for in trying to get this fix? Its also not showing the total mileage anymore which was 96k but now it shows "---------" that.

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