Google-sheets – Working with multiple If statements, data validation and multiple sheets in Google Sheets

function dataValidation() {                                                                                     
var ss = SpreadsheetApp.getActiveSpreadsheet();                                                             
var Tr = ss.getRange("'Body Armor'!C1:C20").getValues(); //Testrange
// Variables and sheetnames
        var b = "'Body Armor'!";                                                                        
        var g = "GS256!" ;
        var gC = "'GS256 Classified'!";
        var h = "B10:B27";
        var l = "B28:B36";
// Get DV ranges
        var gh = ss.getRange(g+h) ;                                                                     
        var ghc = ss.getRange(gC+h);
        var gl = ss.getRange(g+l);                                                                      
        var glc = ss.getRange(gC+l);
// Build DV rules
        var ghr = SpreadsheetApp.newDataValidation().requireValueInRange(gh,true);
        var ghcr = SpreadsheetApp.newDataValidation().requireValueInRange(ghc,true);
        var glr = SpreadsheetApp.newDataValidation().requireValueInRange(gl,true);
        var glcr= SpreadsheetApp.newDataValidation().requireValueInRange(glc,true);
// Loop through each cell
        for(i=0;i<Tr.length;i++) {
                var j = i+1;
                var Hr = ss.getRange(b+"H"+j);
                var Jr = ss.getRange(b+"J"+j);
                var Lr =  ss.getRange(b+"L"+j);
// Test the test range and apply corresponding DV
        if (Tr[i][0] == true) {
                Hr.setDataValidation(ghcr);
                Jr.setDataValidation(ghcr);
                Lr.setDataValidation(glcr);
                }
                else {
                Hr.setDataValidation(ghr);
                Jr.setDataValidation(ghr);
                Lr.setDataValidation(glr);
                }
        }
}

The bounded script includes two onEdit functions this is not a good practice by one hand because this could lead to confusions and by the other only one will be executed usually the one on the last gs file.

Another observation, in this case regarding the code in the question, clearContent syntax doesn't include an argument. In other words, instead of

s.getRange("D4:D18").clearContent(null)

the right syntax is

s.getRange("D4:D18").clearContent();

and instead of

s.getRange("D4:D18").clearContent("D4:D18");

the right syntax is

s.getRange("D4:D18").clearContent();

NOTE: When changing Template!D3 to 2hr Delay the execution transcript shows the following error

Execution failed: Cannot find method clearContent(null). (line 8, file "WIP")