@stef29 

What exactly isn't working and how did you set it up in the ER605 settings?

Here are the instructions I've seen in TP Link documentation.

1. Transmission---->Load Balancing---->Basic Settings Page
   • Check Enable Load Balancing, Click Save
   • Uncheck Enable Application Optimized Routing, Check Enable Bandwidth Based Balancing Routing on ports, check WAN1 and WAN2 (your WAN ports). Then click Save.

  @dsj what's happening is whichever internet connection I add to WAN1 is recognized, link up. Whatever I place in WAN2 is not, link does not connect. I have the settings just as you indicate. Well, had. I went down a path suggested by another site of creating a new LAN with a subnet other than 192.168.0 and was no longer able to login. I did a factory reset per the instructions, lights behaved appropriately, still unable to login. When I'm able to direct connect from a laptop I'll start over. 

  @stef29 

If you are not able to login, it's better try to reboot the PC, special for Windows PC.

Under my experience windows PC always require a reboot to re-obtain IP from the router.

Also ER605 require like 5 minutes to reboot.

I don't know which instruction you refered to, however you may note you don't need to enable Link Backup function. Link Backup will keep backup WAN disconnecting until primary WAN loss Internet

  @stef29 Problem solved, my configuration was mostly correct. The problem was in testing and moving cables around I think things got squirelly with mac addresses. Rebooting the cable modem after connecting it to the ER605 solved that issue. Then I realized another issue was DNS, the netgear wifi router was now using the ER605 address as its DNS server. I changed DNS in the wifi router to Google's DNS and that part was working. I then attached my T-Mobile to the ER605 and have perfectly performing load balancing. So far at least.

To reiterate for anyone else trying this nonsense, I'm sure this will work with other devices and providers.

Cable Modem <-> ER605 WAN port

T-Mobile Gateway <-> ER606 WAN/LAN1 port

ER605 LAN port <-> Netgear Wifi Router WAN port

On the DR605:

• WAN & WAN/LAN1 configured in WAN mode, Dynamic IP
• LAN created with subnet 192.168.10 (just to eliminate using subnet 192.168.0)
• Load Balancing is enabled
• Application Optimized Routing enabled
• Bandwidth Based Balancing disabled
• Link Backup disabled
• Online Detection configured automatic
• Time Zone set to my locale