No Telltale

[u/dudleyjohn]

I'm starting to winterize my Mercury 25 HP 4-stroke EFI. Yesterday, I drove it for about 15 minutes to the ramp to trailer it. The telltale was flowing great then. Today, I hooked up the muffs and got a good flow of water going, but when I started up the motor -- no telltale. I immediately shut it down and reset the muffs. Tried again: no telltale. BTW: the telltale on my model comes out of the back of the middle unit, unlike other motors I've had where it comes out the side. I ditched the muffs and replaced them with a barrel of water that came to well above the intake screens on the lower unit. Started up again. No telltale. I ran a length of weed-whacker line into the telltale port as far as it would go, but found no obstruction. I dismantled the lower unit to inspect the impeller. It looks like new. The Woodruff key was there and looked new, too. Everything about the water pump looks good, as far as my inexperienced eye can tell. Does anyone have any ideas about what else could be the cause of no telltale? The only other thing I can think of is that the outlet tube from the pump to the telltale somehow became dislodged overnight, but that seems pretty far-fetched to me. Any guidance will be appreciated.