ALT light troubleshooting. FIXED, Specifically, what makes it come on? Options

[malcolm2]

I noticed the last time i parked that the red "G" light had come on slightly. Got in yesterday and it was on bright and the volt meter was at 10.5. Revving the engine did not help either.

I checked the belt tension and decided to tighten it.

Took a 20 minute drive to Nashville and all was well. At the last stop i saw the dim G light again. Then bright for a while. Then out.

What is the prognosis? I have about 20k miles on the alt wire harness and gel battery. Maybe 10k on the rebuilt alt.

[Rand]

If you're lucky, it's just dirty contacts at the voltage regulator (rectangular widget on relay board). Try wiggling it, or pull it out and clean the contacts.

My first 914 was doing this. One time while idling with the idiot light on, I wiggled the VR and the light went out. So I shut it down, pulled the VR, cleaned the terminals, and it never happened again. I always like to try the super quick and easy stuff first.

[jim_hoyland]

This write covers your question and a lot more:

http://www.914world.com/bbs2/index.php?showtopic=83309

Good luck with

[jim_hoyland]

Another good source is Ratwell's:

http://www.ratwell.com/technical/ChargingSystem.html

[malcolm2]

I did "search" but rarely found a fix. Lots of trouble shooting but never a break through I started her today and after a 10 minute warm up the light went out. Thanks for the replies I'll keep everyone posted.

[jim_hoyland]

This type of problem has always baffled me too; (IMG:style_emoticons/default/sad.gif)

[bretth]

I haven't had the opportunity to dive into my 914's alternator yet but i recently had an issue with a failing alternator on my Hyndai where the battery was barely charging and in addition to this the alternator warning light was not lighting either. Replacing the alternator fixed the charging issue and the warning light too which confused the hell out of me.

Brett

[malcolm2]

Another good source is Ratwell's:

http://www.ratwell.com/technical/ChargingSystem.html

WOW, that is great. I had forgotten that Ratwell had so much good info. (IMG:style_emoticons/default/piratenanner.gif)

I'll get to the VR tests this afternoon.

Clark

[catsltd]

Mine did the same as your car.Even the 10.5 volt thing.

I replaced all ground straps,added a few more grounds,brand new high output alternator.
Light will stay on for a couple minutes until I can get it out and revving.

I figure its the resistance off the old wires.As soon as I drive for a couple minutes everything is fine,but if I am pulling into garage I will usually get the light to come on again,especially hitting the brake a few times when idle is low.

I know my brake lights have huge resistance and headlights also.
I will be switching to LED if I ever get to just needing cosmetic stuff for my car.LOL.

[malcolm2]

Another good source is Ratwell's:

http://www.ratwell.com/technical/ChargingSystem.html

WOW, that is great. I had forgotten that Ratwell had so much good info. (IMG:style_emoticons/default/piratenanner.gif)

I'll get to the VR tests this afternoon.

Clark

Has anyone done the RATWELL test? I got some crazy numbers. Plus I seem to have an intermittent problem. Once the engine is warm the ALT light goes out at idle. But if I shut it down then restart the warm engine, I get the light on at idle....



RATWELL says to check the voltage at the ALT harness

I took the plastic cover off of the board behind the driver and was able to get my VOM probe into the back of the ALT harness plug as follows.... the black probe was alligator clipped to the battery neg.


Red wire (D+) with the ALT light on and engine idling. I need 14v and I get 1.8v
Grn wire (DF) with ALT light on and engine idling. I need 5.0v and I get 1.8

Red wire again, with the ALT light on and engine reving, I need 14v and I get 1.7v
Grn wire with ALT light on and engine reving, I need 5v and it goes to MAX. If I slowly rev the engine, it creeps past 18volts to 35 volts then the meter goes to --1-----.

Something ain't right, but what is it?

BTW i took emory cloth to the spades for the VR and the ALT harness and cleaned them up.

[Rand]

.....

[malcolm2]

I started her today and after a 10 minute warm up the light went out.

Wait... Before 10 minutes went by, did you try wiggling the VR?? It takes one second to see if that makes the light go out. (IMG:style_emoticons/default/confused24.gif) Letting it warm up for 10 minutes only wastes 10 minutes.

I didn't wiggle it, I pulled it and the ALT wire and touched up the spades with emory cloth. Knocked some white surface corrosion off, but it did not solve my light issue.

[Rand]

[edited] I saw that too late. (IMG:style_emoticons/default/biggrin.gif) You're on it.

[Spoke]

I took the plastic cover off of the board behind the driver and was able to get my VOM probe into the back of the ALT harness plug as follows.... the black probe was alligator clipped to the battery neg.


Red wire (D+) with the ALT light on and engine idling. I need 14v and I get 1.8v
Grn wire (DF) with ALT light on and engine idling. I need 5.0v and I get 1.8

Red wire again, with the ALT light on and engine reving, I need 14v and I get 1.7v
Grn wire with ALT light on and engine reving, I need 5v and it goes to MAX. If I slowly rev the engine, it creeps past 18volts to 35 volts then the meter goes to --1-----.

Something ain't right, but what is it?

BTW i took emory cloth to the spades for the VR and the ALT harness and cleaned them up.

D+ voltage is generated by the alternator and should equal the battery voltage.
DF voltage drives the magnet in the rotor which in turn generates voltage to D+ and charges the car battery.

If the VR is bad, it will not drive DF properly and the alternator may produce too much or too little voltage.

If the alternator is bad, it may not drive V+ (which drives the VR) and the alternator will not charge the battery.

You can test the alternator by removing the VR and shorting D+ to DF. This is equivalent to the VR providing maximum drive current to the rotor magnet. With the car running, the alternator should generate more than 16V. If the alternator doesn't provide >16V and the GEN light stays on, likely the alternator needs replaced.

[malcolm2]

You can test the alternator by removing the VR and shorting D+ to DF. This is equivalent to the VR providing maximum drive current to the rotor magnet. With the car running, the alternator should generate more than 16V. If the alternator doesn't provide >16V and the GEN light stays on, likely the alternator needs replaced.

To be clear,

I remove the VR.

Use a short wire to connect the D+ to the DF female connections on the relay board now visible from removing the VR.

Which should be the 2 that are side by side (or the btm of the triangle formed by the 3 connectors)

VOM on + & - of the battery.
start the car.
read the meter.

So if the ALT gives me >16 volts I can assume I need a VR?

[malcolm2]

I also checked the Ohms on the VR per the Ratwell site...

I also got strange VR continuity test numbers.


site says: I GOT:
•D+ and DF - 0.3 ohms 0.5
•D- an DF - open 83.7
•D- and D+ - 80 ohms 83.3

The problem is he never says what is bad if the readings aren't the same as his. I assume that it is assumed: different readings = bad part.

[Spoke]

You can test the alternator by removing the VR and shorting D+ to DF. This is equivalent to the VR providing maximum drive current to the rotor magnet. With the car running, the alternator should generate more than 16V. If the alternator doesn't provide >16V and the GEN light stays on, likely the alternator needs replaced.

To be clear,

I remove the VR.

Use a short wire to connect the D+ to the DF female connections on the relay board now visible from removing the VR.

Which should be the 2 that are side by side (or the btm of the triangle formed by the 3 connectors)

VOM on + & - of the battery.
start the car.
read the meter.

So if the ALT gives me >16 volts I can assume I need a VR?

Correct, the 2 side by side spades.

Correct on the procedure. What you are doing in effect is fooling the alternator to appear like the VR is trying to maintain maximum charging/voltage output.

If you do get 16+ volts the alternator is able to charge the battery. Even 14+ volts would be good considering if your battery is deeply discharged from not having a functioning electrical charging system.

[Spoke]

site says: I GOT:
•D+ and DF - 0.3 ohms 0.5
•D- an DF - open 83.7
•D- and D+ - 80 ohms 83.3

D+ to DF: not much difference

D- to DF: should be open. There are a diodes between these 2 terminals. This is not a good sign. Try measuring ohms again but reverse the leads of your multimeter. Make D- positive once, then DF positive and see if there's a difference.

D- to D+: not much difference

[malcolm2]

just checking around to purchase a VR, if needed.

What is the deal with the BOSCH unit. $250? the other brands look much different but cost between $20 to $50

Which one are the masses buying for a Daily Driver?

New Bosch (shorter, but similar)


amazon calls it "external", AC / Delco brand I think $30-ish


BERU brand from Germany for $21

[malcolm2]

site says: I GOT:
•D+ and DF - 0.3 ohms 0.5
•D- an DF - open 83.7
•D- and D+ - 80 ohms 83.3

D+ to DF: not much difference

D- to DF: should be open. There are a diodes between these 2 terminals. This is not a good sign. Try measuring ohms again but reverse the leads of your multimeter. Make D- positive once, then DF positive and see if there's a difference.

D- to D+: not much difference

I got 82.7 with red on D- and black on DF same reading with the leads switched.