if i have a strategy that works for me on the ES will it also work on the EUR/USD?
Why do you want to trade EUR/USD (rather than, for example, another index future, or even E6 futures) using a strategy that works for you on ES?
It depends what kind of strategy it is: in my opinion, the faster-moving it is, the more likely it is to "work".
On an intraday basis, for example, there's quite a bit of similarity between the movements of ES and EUR/USD, and from an unlabelled chart it might even be pretty difficult to tell them apart, but if you look at each over a year, the story isn't usually the same at all: indices rise, overall, over the years, but the same isn't true of currency-pairs.
I used to trade EUR/USD and GBP/USD, a long time ago. It was no surprise at all that the strategies that worked for me on those instruments also work for E6 and B6. What was slightly more surprising was that they work just as well for NQ and nearly as well for CL.
Some strategies are more or less "timeless" and can be made to work (at least on an intraday basis) in almost any highly liquid market; others very much less so.
Strictly speaking, it isn't "strategies" that "work", anyway: it's traders.