The backlit nightwatch lights can not be repaired, they are fiber optic lights that are ran through the faceplate by the factory.
As for the squealing, the normal way talkback is installed on these radios is to solder a resistor, 68 oms up to 100 ohms, from the PA to the External speaker on the solder side of the PC board. The more resistance, the lower the talkback volume. Yourse is probably squealing because the resistor is breaking down, I just fixed a radio 2 days ago with the same problem. If you want to remove talkback, just open the case, flip it tothe solder side, and remove that resistor that was installed, or you can replace it with a new resistor and still have talkback.
The meter is fairly easy to replace, you just need to get a new meter, make sure it is one for the Cobra 29 (it will have the 3rd line to show SWR reading, which the Cobra 25 does not). You remove the case screws, the face plate screws, and then remove one screw and loosen the other that hold the meter inplace. You will have to solder the two wires to the new meter, observing which post they came from, this will determine the direction the meter swings. You just remove the light bulb and put it in the new meter casing with the rubber stay. This will be self explanatory when you open the radio.
Now for the dead key. It may have had a swing mod done, which drops the dead key down a couple watts. This is actually a good thing. If you have a lower dead key, this will allow you a larger range of power to swing. You can tell if it has had a swing mod by looking at JP36 to see if there is a jumper or a Capacitor installed. If there is a capacitor, the it has been done. To change back to factory, remove the resistor that was soldered to the solder side, across the capacitor, then remove the capacitor. Now just install a jumper in the place. Here is a link to the Modification Instructions, so you can get a better understanding:
If I left anything out, or you have more questions or need further clarification on anything, don't hesitate to email me firstname.lastname@example.org