1996 GMC Yukon - multiple issues :-(

I am not a certified mechanic, however I am mechanically inclined; so no promises or guaranties, these are just educated guesses.

1. Your battery issues sound as though they could have something to do with the alternator. I don't know if you have had it checked recently or not. The alternator's job is to replenish the battery's charge. The same people that checked your battery can probably check your alternator as well. This is also the most probable cause of your voltmeter's needle showing at 14 then down and again to 12.5. There is a voltage regulator inside of the alternator that is supposed to keep your voltage reading from 13.5 to 14.5.
Other suggestions: ground wires-- the alternator is not able to replenish the charge efficiently enough through old and/or corroded wires. constant short-- something such as the dome light creating an overnight draw on the battery.
The clicking sound you hear could be many different things. There are a lot of solenoids on the vehicle that click when power is presented, such as, the starter solenoid and starter relay. From here, I can not help in stating whether that is good or bad.

2. For your heater situation you may want to check the antifreeze level. Another suggestion is, on some vehicles there is a valve that can be opened or closed along the water/anifreeze line going to your heater core. If the valve is shut, then the water is just bypassing the heater core altogether. It shouldn't take more than five minutes of driving to have your vehicle at operating temp and once there it is much easier for the engine to produce heat than it is to produce cool air. One of the many benefits of physics.

3. I would not worry about the a/c light coming on. If it works don't try and fix it. The bulbs or diodes in question are usually stuck behind a lot of pulling things off.

4. Oil pressure-- there are a lot of factors invloved with what reading you are seeing through the guage. Different oil viscosities will result in differeing pressures. A lighter oil(5w30) will be easier for the engine to push around then a heavier oil(20w50). The heavier the oil the higher the pressure. Also, new oil will be harder to push around then old oil. The newer oil will have the higher pressure. Also, contaminants in the oil will have a bearing on how much oil pressure you have showing. One more that I can think of, oil filters are made differently by different companies. I think that most have check valves in them. The strength of the check valve and whether or not it has one will have an effect on the pressure. I would probably not worry about that until your numbers reach higher or lower extremities.

5. It could have been the culprit. The radiator cap is a fail-safe. It is supposed to be the first thing that goes in the event of too much pressure. fortunately it is also the cheapest thing. Just make sure you get the right pressure rating on the cap. If you get one that is rated below the manufacturer's specs then you will continually be replacing it. (theoretically, depending on driving habits). If you get a cap that is rated above manufacturer's specs then the spring inside the cap may be stronger than your radiator or hoses or waterpump and they instead of the 6 dollar cap will be the first to go.

6. I won't be much help to you on this issue. The only thing I can think of is the transmitter may just be getting weak and may need to be replaced.

I hope this helps

Ok I'll try to help. A bad cell in a battery is not uncommon if the battery has gone completly dead, or gets old. The brake job should not be related to this issue. The clicking could have been the electrical system comming on/off as he connected the battery. If it is still doing it then it is not normal. The difference in the volt meter is normal, and you should not worry about it unless it goes below 12 or above 16 volts. Your oil pressure could be because of normal engine wear. GM oil pressure spec hot in park at idle is 10 lbs min. So you are well within the (healthy) range. A radiator cap can cause a leak, I would watch that closely, for your own protection.The remote door locks work with radio waves. It is possible your teansmitter/key fob is getting weak. There is a module called a RCDLR, remote control door lock reciever. It could be not getting a clear signal, or the reciever antenna could be out. You can get it scaned for codes to see if there are any electronic issues with it. Good Luck

Problem #1 Buy a testlight from an automobile store (it looks lika an ice pick with a wire coming out of the handle; a lightbulb inside.
remove your black (negative battery cable from your battery connect the testlight between the battery cable and the battery post the vehicle should not be running no key in the ignition switch all the doors closed if the hoodlight comes on remove it you want nothing on
in this condition the testlight should not be glowing if it is you have a drain on your battery to find out where remove the door light fuse (so the testlight will not light because the door is open pull out fuses one at a time until the testlight turns off this will be your drain. you can then repair the problem.
next: Batteries should charge about 12.4 to 14.8 volts steady.
If your battery clicked instead of starting your battery was drained.
To test a battery you must load test it at an autoparts store.
a bad cell develops by the evaporation of the water in the cell each cell delivers 2 volts.next: your heater is a small radiator down by your feet; it is fed hot coolant from the radiator by the thermostat so; to be warmer replace the thermostat with one that opens at a cooler temperature they are rated by opening temperature. the AC light is just to let you know it's on it is easily replaced by a shop.
next: your radiator leak should be gone the technicians would have let you kno if there was a problem oil pressure does sometimes fluctuate without causing harm indicator light shold notify you of any trouble.next replace your remote they eventually wear out and, new ones are cheap on e-bay