Hi Guys, I need some help with my sisters TF Solara, her really smart husband decided six months ago that when they replaced their battery not to tighten the negative terminal, please don't ask why I have no idea apart from stupidity. Anyhow the car broke down last night, when I arrived I tightened the negative terminal and the car started straight away, however when she got home she noticed that the battery light was constantly on. I know from looking at other threads that its the charging system in the car that's faulty and its still on with a brand new battery in it. My thoughts were that when the car was running there was no way for the battery to get charge and has overloaded the alternator. All connections on the alternator are fine. I don't have a multi meter to test the output of the battery but am really looking to get peoples thoughts. Can the alternator get stuffed by not having the negative terminal on correctly? Thoughts?

this could be an alternator issue or a regulator issue, without a multimeter its hard to tell, even then it would still be hard to tell, generally it would be a regulator thats gone though.

Before you take out the regulator to check the brushes (just unscrew the two screws), Id look at the alternator fuse... Its a heavy duty fuse in the relay box signified by a battery symbol (there may be two).

+1 on checking the alternator fuse first, this shouldn't have blown but worth a check. Check that the alternator belt is still there too.

Having the negative terminal loose would not normally cause this issue, with the new battery I could be checking the voltage but once again without a MM is near impossible to get an accurate read. If you can get a hold of a voltage regulator easily enough it would be worth a test, generally when these go the prongs on the inside are quite worn. If you have the larger bosch alternator, which you should, the voltage regulator is external and two screws will remove it from the casing, ensure the battery is disconnected or atleast the negative is removed prior to attempting this.

If you have the smaller Mitsi branded alternator the reg is on the inside so a complete alternator swap would be easier.

Battery light probably means the diode pack on the alternator is damaged, it's a fairly cheap replacement part that bolts in easily - try that first. I reckon on 90% chance it will fix the problem - the fault may relate to the previous failed battery overloading the alternator.