Why is the Alternator light on in your VW Beetle?

Answer 1

One of the functions of the alternator regulator is to compare the alternator output with the battery voltage. If there is a problem it puts the light on. Either the battery is overcharging or undercharging or there is an broken earth(ground) cable/strap connection between the bodywork and the engine. Start with the easy and end with the difficult. Take it slow and follow the safety rules in your manual. After every stage, make safe then see if the fault has cleared.

If you have access to one, connect a DC voltmeter or battery tester across the battery. With the engine running there should be a reading of about 13-14.5 volts. It won't be, but should be later. Switch the engine off.

A physical inspection (prod/poke/pull) is always a good place to start. If nothing else you will get to know what the engine bay looks like with everything in place and with the covers off. Whilst looking around check for wiring that comes close to the engine and make sure the insulation hasn't been rubbed/melted away. If all the connections are good and the alternator drive belt is tight, go for the next easiest bit.

Check the connections on the battery and (if not sealed for life) check the battery acid level in each cell, top-up as necessary with distilled/denatured water. If you need to clean the battery connections remove the negative one first. Remove, clean and replace the positive connection then clean and replace the negative connection. A battery has a nominal life of 3 years. Much depends on whether it does a lot of starting/short runs, the climate and range of temperatures it has to endure. In fact, while the battery is disconnected you should take it to your local shop or battery place and get them to test it; normally for free. Also, while the battery is disconnected, check out the cleanliness and security of the cables on the back of the alternator. If the battery is good, the drive belt is tight and the earths are good the only things left are the alternator and loom wiring.

The alternator is a tricky beast and not that easy to diagnose if you don't have the right tackle. Remove it (follow the book) and take it to an auto electric shop/repair facility for testing. If it needs repair they will either sell you the bits, repair it for you or give you an exchange deal on a new or refurbished unit. You could take a chance on one from a breakers but there are no guarantees. On any repair the biggest cost is always labor. Doing it yourself saves money, skins your knuckles and satisfies your soul. You probably won't be able to get the parts at trade cost but you will still get discounts to put a smile on your face. The good news is these faults are rarely loom wiring, they are either connections or big swap out bits.

OpinionWarning Lights

When warning lights turn on [except during starting when the key is in the "start" position] indicates that there is something wrong in that system.

It cannot tell you what is wrong, only that something is not right, and...

You need to have a qualified automotive technician to troubleshoot the electrical system, identify the defect, and properly correct it.