I think the message for building a transformer underground is in line 1763 of simtool.cc.
The same message for the surface is in line 1754.
Since the construction locations for the transformer underground (under the factory) and on the surface (next to the factory) are different, there should be two messages.
Index: trunk/src/simutrans/tool/simtool.cc
===================================================================
--- trunk/src/simutrans/tool/simtool.cc (Revision 11745)
+++ trunk/src/simutrans/tool/simtool.cc (Arbeitskopie)
@@ -1760,7 +1760,7 @@
// underground: first build tunnel tile at coordinate pos
if(underground) {
if(gr->is_water()) {
- return "Transformer only next to factory!";
+ return "Transformer only under the factory!";
}
Thanks for the patch. Since the error message is specific to building an underground transformer under a water factory, I think the error message should mention that. Check r11752.