Need input from a spark chaser here.

I deleted my stock Road King fuel gauge and installed a HD multi-function speedo and now the fuel gauge doesn't work. This is my 2nd of these speedo's but the first one I retained the stock fuel gauge, now with it removed the fuel gauge on the multi-function speedo doesn't work. I'm guessing it is looking for feedback or is in a loop somehow with the stock gauge but I'm no electrician, is there a way to spoof the muti-function speedo into thinking the stock is still installed?

thank you