My 2005 Yukon won't start no lights or horn no power to anything. Battery is fully charged.

check your battery cable connections....

check your cars fuseable link..(cars main fuse)...check your owners manual for location..

I'll try to help, everytime something gets replaced on these yukons, that circuit needs to be RESET ! Is there a reset button, on your steering wheel, to reset a variety of functions ? , check owners manual, or call your dealer for better advise

sound like battery has weak or battery terminals and post need cleaning. have battery charged and checked, if battery good. alternator not charging battery. if battery over 5 years old more likely battery is bad.if battery too weak head lights wont turn on battery dead this time of year if battery old. cold weather will finish it out.

when you turn the key do you hear anything from the starter?

Your battery is to low on power it needs a good charge, or replace it is the best option for a brand new one!

Hello, The Ford systems are real sensitive to Battery fluctuations. You need a fully charged battery to start out with. If the battery is too low and the jump is removed, the car can stop charging.

Ford also made it to reduce the Voltage to the starter. If the battery is low, the Antitheft will reduce the battery voltage to 7 Volts or less.

There are also Relays in the Powerbox. The Ignition Relay may be bad. I understand that the Horn Relay is the same part and if you check the part numbers on the Relays you may be able to use the Horn Relay to get home.

A fully charged battery wil show 13.2-13.6 Volts. All of the Ford, Mercury, and Lincoln vehicles can malfunction like this, so it just isn't your individual car. Your Battery is 5 years old and anything can happen.

I hope my solution is very helpful to you.

check your charging system, your alternator might be on its way out and only works some times

This is definetly the battery, no charge or low charge in the battery, get it checked out.