Tech ruins and tech wonders do not stack with one another even if both are on the same world. However, either will stack multiplicatively with the location/scientist bonus, and the best location/scientist bonus in your empire does NOT need to be at the ruin/wonder location for you to be able to take advantage of this.
I am not certain, but you may need to have a lab of the appropriate type over the ruin/wonder in order to take advantage of the bonus.
The attached screenshot is from a game in which the empire that I'm playing controls all three tech ruins and has built all three tech wonders (the Energy Engineering Facility and Danuta Engineering Facility are on the same world; the other four are each on separate worlds). The empire has a research potential of 1417K and the capacities in each field are 3500 (34% of total) for weapons, 4700 (46% of total) for energy, and 2000 (20% of total) for high tech. The bonuses from scientists/locations are 93% for weapons, 84% for energy, and 89% for high tech. Ruins and wonders each give a bonus of 50%, and I have all three tech wonders and all three tech ruins.
If ruins/wonders do not count towards the actual output, then the outputs we should expect are (empire potential) * (fraction of capacity in field) * (government bonus) * (species bonus) * (scientist/location bonus) ~= 1290K for weapons, 1650K for energy, and 722K for high tech. If ruins/wonders stack with the scientist/location bonus but not with each other, then the outputs we should expect are (empire potential) * (fraction of capacity spent on weapons) * (government bonus) * (species bonus) * (scientist/location bonus) * (ruin/wonder bonus) ~= 1940K for weapons, 2480K for energy, and 1080K for high tech. (Note that all of the numbers reported here have been rounded to three significant digits)
The actual outputs as reported by the game are 1937K for weapons, 2484K for energy, and 1056K for high tech; while there's clearly some rounding error going on, it's pretty clear that the ruin/wonder bonuses stack with the scientist/location bonuses.
Edit: One other thing - I've noticed that occasionally the wonder bonuses won't show up for a while if you've stacked multiple wonders on the same planet.
< Message edited by Aeson -- 1/20/2017 9:19:02 PM >