Object passed over, caused vehicle power failure and animal agitation

At the time of the sighting experience I was working at a horse farm in Tx. The other person with me at the time of sighting was the trainer at the same farm.
Myself and the other person were transporting a load of 6 horses from a farm in Houston to our base farm in Waco Tx at night.  Around 10:15 pm we pulled over to check the horses, water them ( it was a very warm night)  We opened up the side door of the transport and proceeded to tend to the horses. We were driving a semi tractor trailer type transport 
A few minutes later we noticed the horse getting agitated, ears flicking back and forth, breathing heavier, stomping their hooves. The other person stepped out of the transport  to see if there was a coyote or something they caught scent of, he saw nothing.  The horses agitation increased 
At around 10:30  my companion called me to come outside the trailer I did. He pointed up to the sky, northwest direction, I looked. There was a patch of the sky that was darker than the rest, and the stars were blocked out. It appeared to be moving towards us in a southeast direction At that time the semi started to run roughly, the lights started to dim all over it and inside the trailer. The horses were quite agitated at this point.
The dark spot in the sky was now almost overhead and we were aware it was a triangle shape, and very large. In my estimation it was over 2 football fields long, or over the length of my outreached hand to the sky, I did that to try to judge the size.
As it passed overhead there was no sound. It was definitely a solid object, had a appearence of metal, possibly stone, or another hard surface. And as it passed over  the semi tractor trailer ceased running,like the fuel wasn't getting to the engine and the lights faded  to going totally off. The horses were very nervous by this time.
After approx. 10 minutes ( the object moved slowly) it had passed completely over us and was heading in the southeast direction still.  As it got farther away the semi tractor trailer started back up, the lights came back on, both gradually as if they were filling from being drained off or something. the horses settled as it got farther away as well.
Both of us were shaken at this experience, and have never forgotten it to this day  We watched the object until it disappeared from decent view which was around 11pm  then closed up the trailer, and proceeded on our way to Waco.
Neither of us have spoken or reported this until this past year. Only to the Coast to Coast radio website, and have told a few close friends.
Witness indicates that date of sighting is approximate.  PD