Using Visual Studio AS Git Merge Tool

.gitconfig

[diff]
	tool = vsdiffmerge
[difftool]
	prompt = true
[merge]
	tool = vsdiffmerge
[mergetool]
	prompt = true
[difftool "vsdiffmerge"]
	cmd = \"C:\\Program Files (x86)\\Microsoft Visual Studio\\2017\\Enterprise\\Common7\\IDE\\CommonExtensions\\Microsoft\\TeamFoundation\\Team Explorer\\vsdiffmerge.exe\" \"$LOCAL\" \"$REMOTE\" //ignorespace //t
	keepBackup = false
[mergetool "vsdiffmerge"]
	cmd = \"C:\\Program Files (x86)\\Microsoft Visual Studio\\2017\\Enterprise\\Common7\\IDE\\CommonExtensions\\Microsoft\\TeamFoundation\\Team Explorer\\vsdiffmerge.exe\" \"$REMOTE\" \"$LOCAL\" \"$BASE\" \"$MERGED\" //ignorespace //m
	keepBackup = false
	trustExitCode = true

MergeToolChooserConfig.xml

<?xml version="1.0" encoding="utf-8" ?>
<MergeToolChooserConfig>
  <!-- TDS Item Merge Tool -->
  <MergeTool Extension=".item" Cmd=".\SitecoreItemMerge.exe" Parameters="&quot;$1&quot; &quot;$2&quot; &quot;$3&quot; &quot;$4&quot;"/>
  <!-- Default entry -->
  <MergeTool Cmd="C:\\Program Files (x86)\\Microsoft Visual Studio\\2017\\Enterprise\\Common7\\IDE\\CommonExtensions\\Microsoft\\TeamFoundation\\Team Explorer\\vsdiffmerge.exe" Parameters="&quot;$1&quot; &quot;$2&quot; &quot;$3&quot; &quot;$4&quot; //ignorespace //m"/>
</MergeToolChooserConfig>

tds.gitconfig

[diff]
	tool = vsdiffmerge
[difftool]
	prompt = true
[merge]
#	tool = vsdiffmerge // Commented out because we're switching over to TDS Switcher
	tool = merge_chooser
[mergetool]
	prompt = true
[difftool "vsdiffmerge"]
	cmd = \"C:\\Program Files (x86)\\Microsoft Visual Studio\\2017\\Enterprise\\Common7\\IDE\\CommonExtensions\\Microsoft\\TeamFoundation\\Team Explorer\\vsdiffmerge.exe\" \"$LOCAL\" \"$REMOTE\" //ignorespace //t
	keepBackup = false
[mergetool "vsdiffmerge"]
	cmd = \"C:\\Program Files (x86)\\Microsoft Visual Studio\\2017\\Enterprise\\Common7\\IDE\\CommonExtensions\\Microsoft\\TeamFoundation\\Team Explorer\\vsdiffmerge.exe\" \"$REMOTE\" \"$LOCAL\" \"$BASE\" \"$MERGED\" //ignorespace //m
	keepBackup = false
	trustExitCode = true
[mergetool "merge_chooser"]
    cmd = \"C:\\Program Files (x86)\\Hedgehog Development\\Team Development for Sitecore (VS2017)\\MergeToolChooser.exe\" \"$BASE\" \"$LOCAL\" \"$REMOTE\" \"$MERGED\"

Global .gitconfig location is -

C:\Users[username].gitconfig