Exchange Hybrid Configuration Wizard - Error 1603 - Connector registration failed

We faced the same issue and adding the registery keys mentioned didn't help for us.

the resolution for us was enabling tls 1.2

checking if tls 1.2 is enabled:

Function Get-ADSyncToolsTls12RegValue
{
    [CmdletBinding()]
    Param
    (
        # Registry Path
        [Parameter(Mandatory=$true,
                   Position=0)]
        [string]
        $RegPath,

        # Registry Name
        [Parameter(Mandatory=$true,
                   Position=1)]
        [string]
        $RegName
    )
    $regItem = Get-ItemProperty -Path $RegPath -Name $RegName -ErrorAction Ignore
    $output = "" | select Path,Name,Value
    $output.Path = $RegPath
    $output.Name = $RegName

    If ($regItem -eq $null)
    {
        $output.Value = "Not Found"
    }
    Else
    {
        $output.Value = $regItem.$RegName
    }
    $output
}

$regSettings = @()
$regKey = 'HKLM:\SOFTWARE\WOW6432Node\Microsoft\.NETFramework\v4.0.30319'
$regSettings += Get-ADSyncToolsTls12RegValue $regKey 'SystemDefaultTlsVersions'
$regSettings += Get-ADSyncToolsTls12RegValue $regKey 'SchUseStrongCrypto'

$regKey = 'HKLM:\SOFTWARE\Microsoft\.NETFramework\v4.0.30319'
$regSettings += Get-ADSyncToolsTls12RegValue $regKey 'SystemDefaultTlsVersions'
$regSettings += Get-ADSyncToolsTls12RegValue $regKey 'SchUseStrongCrypto'

$regKey = 'HKLM:\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.2\Server'
$regSettings += Get-ADSyncToolsTls12RegValue $regKey 'Enabled'
$regSettings += Get-ADSyncToolsTls12RegValue $regKey 'DisabledByDefault'

$regKey = 'HKLM:\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.2\Client'
$regSettings += Get-ADSyncToolsTls12RegValue $regKey 'Enabled'
$regSettings += Get-ADSyncToolsTls12RegValue $regKey 'DisabledByDefault'

$regSettings

enable TLS 1.2

If (-Not (Test-Path 'HKLM:\SOFTWARE\WOW6432Node\Microsoft\.NETFramework\v4.0.30319'))
{
    New-Item 'HKLM:\SOFTWARE\WOW6432Node\Microsoft\.NETFramework\v4.0.30319' -Force | Out-Null
}
New-ItemProperty -Path 'HKLM:\SOFTWARE\WOW6432Node\Microsoft\.NETFramework\v4.0.30319' -Name 'SystemDefaultTlsVersions' -Value '1' -PropertyType 'DWord' -Force | Out-Null
New-ItemProperty -Path 'HKLM:\SOFTWARE\WOW6432Node\Microsoft\.NETFramework\v4.0.30319' -Name 'SchUseStrongCrypto' -Value '1' -PropertyType 'DWord' -Force | Out-Null

If (-Not (Test-Path 'HKLM:\SOFTWARE\Microsoft\.NETFramework\v4.0.30319'))
{
    New-Item 'HKLM:\SOFTWARE\Microsoft\.NETFramework\v4.0.30319' -Force | Out-Null
}
New-ItemProperty -Path 'HKLM:\SOFTWARE\Microsoft\.NETFramework\v4.0.30319' -Name 'SystemDefaultTlsVersions' -Value '1' -PropertyType 'DWord' -Force | Out-Null
New-ItemProperty -Path 'HKLM:\SOFTWARE\Microsoft\.NETFramework\v4.0.30319' -Name 'SchUseStrongCrypto' -Value '1' -PropertyType 'DWord' -Force | Out-Null

If (-Not (Test-Path 'HKLM:\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.2\Server'))
{
    New-Item 'HKLM:\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.2\Server' -Force | Out-Null
}
New-ItemProperty -Path 'HKLM:\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.2\Server' -Name 'Enabled' -Value '1' -PropertyType 'DWord' -Force | Out-Null
New-ItemProperty -Path 'HKLM:\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.2\Server' -Name 'DisabledByDefault' -Value '0' -PropertyType 'DWord' -Force | Out-Null

If (-Not (Test-Path 'HKLM:\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.2\Client'))
{
    New-Item 'HKLM:\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.2\Client' -Force | Out-Null
}
New-ItemProperty -Path 'HKLM:\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.2\Client' -Name 'Enabled' -Value '1' -PropertyType 'DWord' -Force | Out-Null
New-ItemProperty -Path 'HKLM:\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.2\Client' -Name 'DisabledByDefault' -Value '0' -PropertyType 'DWord' -Force | Out-Null

Write-Host 'TLS 1.2 has been enabled. You must restart the Windows Server for the changes to take affect.' -ForegroundColor Cyan

Téva Paofai Thanks a lot, this fixed my issue 🙂