I've had trouble moving from DCS v1.5 to v2.5 so wanted to keep v1.5 working but alas it finally failed when I migrated to Windows 10, and I was stuck with v2.5.
Recently I discovered that v1.5 is working again, but I had already migrated to v2.5, so now to get Helios working again on v1.5.
Helios application works by interacting with DCS via lua script files, merely text files that direct DCS to do certain things like where to display the screen, and how to send and receive data from the Helios profile/ screen interface.
The 2 or 3 main files are:1. export.lua
For 1.5 C:\Users\%Username%\Saved Games\DCS.1_5\Scripts
For 2.5 C:\Users\%Username%\Saved Games\DCS\Scripts2. a monitor lua file
(the user creates or modifies it to send the game display to the monitor or monitors for your setup. This file can be called anything you like mine Biggerhog37, but in order to work you must select that monitor configuration from within DCS
For my v2.5 located C:\Program Files\Eagle Dynamics\DCS World\Config\MonitorSetup
For my v1.5 located D:\Program Files\Eagle Dynamics\DCS World 1.5\Config\MonitorSetup
Notice that the name of the configuration that appears in DCS options is NOT the file name of the monitor .lua but rather the name that appears inside the monitor .lua file at the top of the file, so must open the lua file to edit the name that will appear in DCS. In my case the name of the file and the name within the lua file are the same, but they needn't be. DCS will display the name within the file not the file name.3. Options.lua
This file saves the selected configuration with DCS so when DCS starts it displays the game on the correct monitor monitors. If after changing your monitor configuration you can not click a menu item because its off screen, changing the monitor option in this file will allow you to revert the display to the default configuration. To do this edit the options.lua file save it and start DCS again, it will read the file and change back the display to a default configuration.
If the display is not where it should be, edit the monitor lua file
If the display is correct but the gauges aren't working the export.lua file is the wrong file. Make sure the export.lua file is where its supposed to be (see above)
The default export.lua file in my version of DCS is 14K, but the version I use is 258K, obviously the default is too small to drive all the requirements of Helios. I see Capt Zeens newest lua file is 592K.
See images below