The Horse born in 12-10-78 belongs to Earth element not Wood. 19/12//66 belongs to fire Horse.
In Chinese zodiac, there are four zodiac signs that create a self-inflicting problem of obstruction include Dragon, Horse, Rooster and Pig. So, two horses will have problems if stay together or cooperate with each other. They are easy to have confilicts. Luckily, fire and earth are compatible in five elements, it's said the Fire creates Earth. So, Although there is some problems between the two, the boss can be a promoter to the wood horse.
19/12//66 belongs to fire Horse.
In Chinese zodiac, there are four zodiac signs that create a self-inflicting problem of obstruction include Dragon, Horse, Rooster and Pig. So, two horses will have problems if stay together or cooperate with each other. They are easy to have confilicts. Luckily, fire and earth are compatible in five elements, it's said the Fire creates Earth. So, Although there is some problems between the two, the boss can be a promoter to the wood horse.