Battery/alternator charge issues

Post by **abscate** » 21 Aug 2020, 04:13

Measure the voltage at each end of the cables with the lights on. The voltages should be within 0.1V on each end

Mstrshkbrnnn · Post by **Mstrshkbrnnn** » 21 Aug 2020, 22:52

misha wrote: 21 Aug 2020, 02:35 Thin wire is a signal wire for warning lamp and it's "awakening" for the alt.
Without it or if it's shorted somewhere...alt will not have an output.

is there a way I can test the thin wire to see if it’s shorted? I know that the alternator does not have any output.

Post by **misha** » 22 Aug 2020, 02:18

Do you have battery warning light with key in pos.II(bulb check)?
Is it ON while engine is running?

Post by **jimmy57** » 22 Aug 2020, 11:04

The warning light wire does two things: it provides current flow (exciter feed in alternator-speak) that makes the rotor (belt spun part of alt) magnetic so the initial charging starts when engine speed gets to 600 RPM or thereabouts. Once the alternator is producing current flow then there is a diode set that that taps into stator wiring and provides current the voltage regulator uses to continue the current flow to rotor for charging. Actually the voltage regulator controls this rotor current to regulator alternator output. If you unplug the small gauge wire from back of alternator and turn on ignition you should have few warning lights lit. Now reach down and plug that wire back onto the spade terminal it came from and look to see if the alternator and a few other warning lights come on. If those warning lights are on with the small gauge wire disconnected then there is a short to ground tuning those lights on and not the alternator effectively ground those bulbs through the rotor windings via brushes. These last points are what Misha was directing you to check. If the wire is grounded then if you leave it unplugged from alternator and then start engine and rev it past about 3500 RPM the alternator will charge. There is a faint residual magnetism in the rotor and if the rotor is spun fast enough that will produce enough current flow and the alternator will start without the exciter feed. Newer cars with much more complicated electrical systems and alternators that are variable and sometimes turned off, do the exciter supply differently.

Mstrshkbrnnn · Post by **Mstrshkbrnnn** » 23 Aug 2020, 16:13

misha wrote: 22 Aug 2020, 02:18 Do you have battery warning light with key in pos.II(bulb check)?
Is it ON while engine is running?

All warning lights are on w the key in on position, and with engine running. Only lights that turn off once the engine is started/running are the oil pressure and transmission arrow lights.

Mstrshkbrnnn · Post by **Mstrshkbrnnn** » 23 Aug 2020, 16:18

In response to jimmy, sorry it took me reading your post at least 5 times before I understood what you were saying lol. If I understood correctly, most of my warning lights should be off if the thin wire at the back of the alternator disconnected right? If they remain on with the wire disconnected, then that means it’s grounded out somewhere else correct?

Post by **misha** » 23 Aug 2020, 16:50

If you have battery warning light ON,along with all other lights on bulb check with key in pos.II,thin wire is ok.

Alternator or voltage regulator is faulty.

I would remove it and take it to a car electrician to have it tested.
Then you will know if you need a replacement alternator or just a voltage regulator.

On Bosch alternators....usually...it's voltage regulator that goes bad.