Uniden UH7760NB Remote Head UHF

Howard
There must be a mode selection activated to select one speaker HH, or both or the other indash only.
Possibly pushing buttons is changing it's mode of operation. Maybe, find that button and don't tough it when set.

When transmit is working, there should be a symbol on the screen to show. Is that always working or is it sometimes not active when the TX/PTT button is pushed?

If you push the PTT button and it doesn't work, ie no change on screen, then you may have a faulty PTT button, Mic lead or connection to the unit in the dash.
Give things a wriggle when you transmit to see if it drops out or in of TX with the fiddling around.
You may discover the area where the problem is, or the situation which causes it.

You could check your plug connections. Pull them apart and then re-mate them making sure they go right home..

Howard,

From what I can find on this model, it seems that both the speaker in the base unit and the speaker in the hand-held unit always operate simultaneously. There is no option. Uniden use the phrase "Dual Speaker with Synchronised Volume (Speaker at Base and MIC)" which seems to support my findings.

That's right Allan, no options, the sounds comes out of the hand mic speaker and the unit speaker.

I have my unit mounted on the trans hump just out of the way of my left leg, so I get the sound clearer from there . . . but also there's a jack in the unit you can plug an external speaker into and place a good aftermarket speaker on the dash or wherever.
Like this . . . http://www.prestigecom.net.au/Benelec-Communications-Speaker
Makes things a lot clearer :)

As for transmission issue.
I haven't had any problems with mine (3 years), suggest check handset connection to unit to see if correctly attached.
Then get a hand held and a wife / mate, and give it a good testing.

If the handset or unit is faulty, I suspect the Auto Elec wouldn't be the one to talk to, but the retailer from where it was purchased.