Alternator Not Charging

[REman]

Good Morning,

Wondering if someone can confirm the following statement from the "Tech FAQ's" under electrical heading...

"3.Open charge light in dash (does it light when you turn the key on?) or blue wire to charge lamp broken or unplugged - if the lamp or blue wire is open, the alternator WILL NOT CHARGE."

I don't think my warning light has worked for years but just last week realized my alternator is not charging after a couple no starts and getting jump started and after doing all the tests with a multimeter and not seeing a warning light come on. So after reading the above statement I figured I should test the dash bulb itself for the batt/alternator warning light just in case. I confirmed it works after pulling the instrument cluster and the bulb in its socket holder and testing it. In the process of pulling bulb socket out I broke off one of the wire contacts that press fit onto the socket/bulb holder, and am wondering if I really need this warning light for alternator to function since it hasn't worked for a long time? It looks like a real PITA to try and solder/repair back to working order.

[Mike W.]

Technically you do need the light to complete the circuit to the regulator to start the charging process. But... I have seen some self exciting alternators, yes, Bosch BMW E12 applications, so it's conceivable you might not need the light for it to work even though you should need it for the charging process to start. And it's only used when charging starts, that fraction of a second where it starts turning fast enough, voltage is applied and it starts charging.

Obviously break out a meter and see if it is charging or not, touch a wire from hot to the blue wire on the alternator and see if it starts charging. Not sure how likely, but it's possible the regulator is bad and or the brushes in it have worn away and wont allow charging. So again, it's possible, not likely, but possible a new or repaired regulator might fix things. Still bad to not have any warning of no charge or in case of a broken belt the water pump not even turning.

[Robert Bondi]

Yeah, there are plenty of workarounds, but you do need that voltage drop there in a closed circuit to start the alternator. A workaround could be wiring another bulb or resistor in place of the instrument cluster bulb. I think it's the only thing in the cluster that's more than just driver information. Unfortunately, all the cluster electronics depend on making contacts to that thin copper flex interconnect that is likely showing its age on most cars.

[REman]

Thanks for the quick responses guys, helpful to understand the electronics around it.
I remember having strange squeaks when the engine first started up for a long while there all along thinking it was belts when could have been the bearings maybe in the alternator causing it. The belt is still turning though so maybe not.

Years ago I replace my cracked instrument cluster from a donor car and kept the old one so I may try to take that cluster of copper wires and see if I can implement it in the current one.

Thanks again.

[REman]

Update: I was able to replace the cluster of wire connections on the right side of the instrument cluster successfully from my old one, it was easier than I thought the first time I looked at it because it is fixed in a dedicated harness with basically 3 screws holding it and careful not to break the attached temperature gauge as I was pulling it out and putting it on.

Still not getting the batt. dash light to come on so I hotwired the blue wire as you suggested Mike, from the alternator to the positive post on the battery. and the batt. dash light came on (so I know it functions now) with ignition off. I started the engine and it went off so I tested to see if I was getting a charge from the alternator but was only getting the battery reading of 12.1-12.5V at idle and a little over 1500 RPM as before. Not the 13.5-14.5 as needed. Still wondering why the batt. dash light won't come on as before without being hotwired and looking for a replacement alternator since I need to replace my housing too, where a piece broke off a long time ago at the top where it bolts on.

[Mike W.]

I would throw a voltage regulator at it. Rarely, but I've had it happen, the regulator can fail and not light up the light on the cluster, but cause a no charge condition. Plus they're cheap and easy to change, you've got little to lose. 15-20 bucks and 5 minutes to change. Worth rolling the dice to me.

[REman]

You did it again Mike, that's what it was! I had a voltage regular in my spare parts box and removed and replaced with success.
One of the brushes wasn't making contact (most likely the spring broke).and shut things down. Getting the voltage needed now and my dash light works too!

Thanks a bunch Mike!!