Looks like I'm stuck again

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I have a Dish500 dish setup. It's receiving 82w & 91w. Signal is fine, checked with a meter. I have the line coming down and into a Diplexer so it combines the satellite signal with the cable signal. Then at the receiver I have the other Diplexer to uncombine the signals. It works fine, but when I add a
DiSEqC Switch at the lnb's it doesn't switch between the two lnb's. It stays on the first one it locks onto.
My guess is the switch is not receiving commands from the receiver because of the Diplexers. Does that sound right and is there some way I can get it to work?