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Mon Aug 11, 2014 6:45 pm

My alternator (G) light slowly starts to come on as I reach higher RPM's on the bus. It usually starts glowing around 60 MPH. I pulled over and revved up the engine and the same thing happened at higher RPM's. I took a look around the forum and didn't see anything specifically like this but if someone has an idea or a link to a thread with a similar issue I'd much appreciate it.

Engine was just rebuilt including the alternator being refurbished. 2.0 engine with one of the 65/70 AMP alternators if that helps.

Thanks!

Scott

Mon Aug 11, 2014 7:02 pm

Since the brushes are apparently (hopefully) new we can rule out worn brushes, either the commutator is bumpy/out of round or the brushes haven't fully seated yet, hopefully they just need to wear in a bit.

Are those 60 MPH heading in a westerly direction Scott?

Mon Aug 11, 2014 7:10 pm

busdaddy wrote: Since the brushes are apparently (hopefully) new we can rule out worn brushes, either the commutator is bumpy/out of round or the brushes haven't fully seated yet, hopefully they just need to wear in a bit.

Are those 60 MPH heading in a westerly direction Scott?

When I first got the bus back it wasn't doing this but has started to over the past few weeks. In that time I replaced the ground wire to the starter battery and also installed my aux battery using an ACR to separate the two banks. I'm not sure if any of that would have an effect on the light coming on but seeing as it's electrical it's worth a mention. I'm taking the bus out to the mechanic tomorrow for a valve adjustment so maybe I'll just get him to look at it.

As for heading west, I'll be leaving Manitoba in roughly two weeks give or take so I'm hoping to be in BC towards the start of September. We can finally enjoy a cold beer or pop or whatever you drink.

Mon Aug 11, 2014 7:43 pm

wanderglobe wrote: We can finally enjoy a cold beer or pop or whatever you drink.
I'm on it like a fat kid on a Smartie!! :D

Having a mechanic look at the brushes will be a couple hour job and hopefully you aren't financing his education on how to dismantle an alternator too. The light says there is a difference between the alternator output and the system voltage up front at the back of the dash. Maybe try one of those volt meters you plug into the cig lighter to confirm it's alternator output that's dropping off at speed because there's a tiny chance it's a bad regulator letting it severly overcharge. A Volt/OHM meter from Princess auto and some alligator test leads will also do and be very handy when on the road later.

Mon Aug 11, 2014 8:44 pm

busdaddy wrote: wanderglobe wrote: We can finally enjoy a cold beer or pop or whatever you drink.
I'm on it like a fat kid on a Smartie!! :D

Having a mechanic look at the brushes will be a couple hour job and hopefully you aren't financing his education on how to dismantle an alternator too. The light says there is a difference between the alternator output and the system voltage up front at the back of the dash. Maybe try one of those volt meters you plug into the cig lighter to confirm it's alternator output that's dropping off at speed because there's a tiny chance it's a bad regulator letting it severly overcharge. A Volt/OHM meter from Princess auto and some alligator test leads will also do and be very handy when on the road later.

Good news is it's a VW mechanic. Same fellow who just did my entire rebuild so he's experienced with these things and has the tools. Before I drive out tomorrow I'll disconnect the cable running to the aux battery and see if that has any effect. :)

Fat kid on a smartie. haha

Tue Aug 12, 2014 9:13 am

you can have him check voltage with a volt meter. You should have 13.5 - 14.5 volts DC +/- at RPM and minimal AC, meaning in the millivolts AC. If you have bad diode(s) in the alternator that will cause AC voltage to jump up, and cause the symptoms you have with the light. If so the fix is to replace the alternator. (If it is a 70 amp, I believe that the diode plates are NLA.)

Tue Aug 12, 2014 12:27 pm

SGKent wrote: you can have him check voltage with a volt meter. You should have 13.5 - 14.5 volts DC +/- at RPM and minimal AC, meaning in the millivolts AC. If you have bad diode(s) in the alternator that will cause AC voltage to jump up, and cause the symptoms you have with the light. If so the fix is to replace the alternator. (If it is a 70 amp, I believe that the diode plates are NLA.)

I hope that's not the issue. The alternator was just refurbished and tested by a local shop. They would pick up on something like that wouldn't they?

Tue Aug 12, 2014 1:02 pm

wanderglobe wrote: SGKent wrote: you can have him check voltage with a volt meter. You should have 13.5 - 14.5 volts DC +/- at RPM and minimal AC, meaning in the millivolts AC. If you have bad diode(s) in the alternator that will cause AC voltage to jump up, and cause the symptoms you have with the light. If so the fix is to replace the alternator. (If it is a 70 amp, I believe that the diode plates are NLA.)

I hope that's not the issue. The alternator was just refurbished and tested by a local shop. They would pick up on something like that wouldn't they?

it could have gone bad after it was installed. Someone could have for example hooked up wires backwards even for a moment.

Wed Aug 13, 2014 8:28 am

I would think the voltage regulator would be more likely than the alternator..

Wed Aug 13, 2014 9:27 am

A few minutes with a voltmeter will answer most questions.

- Measure the battery voltage with the engine turning around 3000 rev/min. It should not exceed 14.4 volts or so. If it does, the regulator is likely toast. Disconnect it and try again. If the voltage is still high, then either the alternator is goofy or there's shorts in the alternator harness.

- If the battery voltage is OK, then measure the voltage on either side of the ALT indicator on the dash, and note what wire has what voltage.

The ALT indicator can only illuminate if there's a voltage differential across it. Normally, both the blue and black wires are at battery voltage. Generally, on a failure, the blue wire is below 12 volts. Sometimes, due to bad wiring connections, bad fuse connections, or a bad ignition switch, the blue wire is normal and the black wire is below 12 volts.

Wed Aug 13, 2014 2:11 pm

Turns out it was some corrosion and a faulty wire causing the problems. The light still comes on but just ever so barely. You have to put your hand around it to see it. Very dim. Voltage output and everything else was fine. Thanks for all the help and the replies. Very much appreciated.

Scott

Wed Aug 13, 2014 2:44 pm

If the light is still glowing, even if just slightly it doesn't sound fixed.

Sun Sep 14, 2014 8:30 pm

I'm having the same issue. High revs cause the light to come on. Same engine, 2.0 L, same 70 amp alt. I had it rebuilt at a local shop and probably have around 15k miles on it. I have checked all connections (batt cables, frame grounds, starter connections) I have replaced the VR with a new solid state Hella unit. No difference what so ever. I get random flashes especially if I rev it. Sometimes the light will stay on and it will take a couple revs to make it go off. Can brushes get sticky and have intermittent contact??

After reading this thread it sounds like the diodes could have an issue. Worst part is that my local re-builder (who I have used since high school) recently closed up shop.

So Scott, just some wire clean up and you were good?? I didn't have a dim lit Alt light before this, never had big Alt issues really. I have some 55 amp units here at the house, but don't really want to down grade and I don't really want to pull the fan and change out the cooling boot.

Any ideas would be helpful

Sun Sep 14, 2014 10:39 pm

jmstu76 wrote: I'm having the same issue. High revs cause the light to come on. Same engine, 2.0 L, same 70 amp alt. I had it rebuilt at a local shop and probably have around 15k miles on it. I have checked all connections (batt cables, frame grounds, starter connections) I have replaced the VR with a new solid state Hella unit. No difference what so ever. I get random flashes especially if I rev it. Sometimes the light will stay on and it will take a couple revs to make it go off. Can brushes get sticky and have intermittent contact??

After reading this thread it sounds like the diodes could have an issue. Worst part is that my local re-builder (who I have used since high school) recently closed up shop.

So Scott, just some wire clean up and you were good?? I didn't have a dim lit Alt light before this, never had big Alt issues really. I have some 55 amp units here at the house, but don't really want to down grade and I don't really want to pull the fan and change out the cooling boot.

Any ideas would be helpful

Turns out the alterenator, despite having just been rebuilt, was done. Not wrong what was wrong but there was no fixing it. Had to get a new one.

Mon Sep 15, 2014 8:23 am

wanderglobe wrote: jmstu76 wrote: I'm having the same issue. High revs cause the light to come on. Same engine, 2.0 L, same 70 amp alt. I had it rebuilt at a local shop and probably have around 15k miles on it. I have checked all connections (batt cables, frame grounds, starter connections) I have replaced the VR with a new solid state Hella unit. No difference what so ever. I get random flashes especially if I rev it. Sometimes the light will stay on and it will take a couple revs to make it go off. Can brushes get sticky and have intermittent contact??

After reading this thread it sounds like the diodes could have an issue. Worst part is that my local re-builder (who I have used since high school) recently closed up shop.

So Scott, just some wire clean up and you were good?? I didn't have a dim lit Alt light before this, never had big Alt issues really. I have some 55 amp units here at the house, but don't really want to down grade and I don't really want to pull the fan and change out the cooling boot.

Any ideas would be helpful

Turns out the alterenator, despite having just been rebuilt, was done. Not wrong what was wrong but there was no fixing it. Had to get a new one.

Well, I was afraid of that. It is the next logical step though.