Please guys.....!

For days,i'm desperately trying to transform into google coordinates,ww2 english coordinates...
I have absolutely no problem with US ones.Always good results when I spot combat zones to my friends French diggers...
Yours,i'm everytime failing !
No sites to explain me where i'm wrong!And i'm sad cause i found a wonderful war diary full of coordinates,describing the battle in and aroundLingevres with the 50th Division in June 44.
The problem is hard to explain with my bad English:my reference grid is not the good one,altough I 'm using the one adopted for this area of France by all the Allied armies:French Lambert Zone 1.
The geo coordinates found in this Diary,once traduced in google vocabulary,drop me in the center of Brittany...on a June the 14th 1944...Impossible,isn't it...
If you could send me a link where i could find explanations,you would be gentlemen!
Many thanks!!