I've been having weird electrical things happening like my speedo works on and off,and the engine idles really high,low or fine.
I checked the ground wires but lately I noticed when driving at night the light will dim and my volt meter gauge will go down to 11-12 and then it will go back up to 13-14 volts and the lights will go bright. This happens maybe 5 times on a 15 minute drive.
Could it be the alternator or maybe a bad connection?
The car has 105kms and the alternator was replaced at 60kms.

 

you really can't rely on the factory guages for much of anything. Verify it with a meter on the battery. With the car off, you should see 12.5v, and with it running you should see about 14.3. It could be quite a few things, and I don't think any of them would be related to the speedo. It could be the voltage regulator in the alternator going out, it could be a bad ground somewhere in the charging system, or a faulty connection maybe on the wire that carries the power away from the alternator or the 12+ terminal on the starter (the car's power feeds off that terminal).

Check out that stuff and let us know how it goes

Matt