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New alternator (90 or 65 amp) OR is alt ok? SOLVED
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bobhill8
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PostPosted: Mon Oct 08, 2018 9:59 am    Post subject: New alternator (90 or 65 amp) OR is alt ok? SOLVED Reply with quote

Hey - Reading only 12V at the positive terminal of the alternator with the engine running. Checked the tightness of the belt and connections. Battery was load tested by NAPA and is solid. Assuming I need a new alternator, do I go with the 90 or 65 amp, since I have the A/C unit disconnected and removed. 1986 2WD. Thanks.
PS - since I am getting 12V at the + terminal, does that rule out the Voltage Regulator as a problem?


Last edited by bobhill8 on Wed Oct 17, 2018 5:05 pm; edited 2 times in total
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crazyvwvanman
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PostPosted: Mon Oct 08, 2018 10:04 am    Post subject: Re: which new alternator (90 or 65 amp) ? Reply with quote

You should see 14v at the alternator with engine running, not 12v. It often says it right on the alternator and on the voltage regulator.

What about your charging led on the dash? Is it working properly?

When you turn on the key the red bat led should come on solid. Then after the engine is running it should turn off. You may have to tap the gas pedal first. Does it do this?

Mark
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MarkWard
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PostPosted: Mon Oct 08, 2018 10:22 am    Post subject: Re: which new alternator (90 or 65 amp) ? Reply with quote

Camper or passenger van? If you are not trying to camp, the 65amp will be fine for maintaining a starting battery, but if you want to recharge batteries, the larger alternator would be a better choice. You also need to pay attention that your alternator harness matches the alternator you buy. I would verify your charging light operation based on Mark's description. The alternator uses that circuit to excite the alternator into charging.
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bobhill8
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PostPosted: Mon Oct 08, 2018 10:42 am    Post subject: Re: which new alternator (90 or 65 amp) ? Reply with quote

Thanks guys, More info. I do have an aftermarket LED battery voltmeter on the dash, so I knew that something was wrong. In the past when I first start normally, I need to hit the gas a bit to get the alternator to kick in. That no longer works. The reading I am getting at the battery matches that with the LED display. With the engine running, even after revving, I'm stuck at 11.9 or 12. That would normally pop up to 13.3 or 13.4 I took off the VR and it looks fine with both brushes only slightly worn and with plenty of spring in them.

Thanks Mark - I have a camper and additional battery, so it seems that 90 is the answer.

Can you confirm that putting the positive of the multimeter on the post of the alternator directly and the black to ground is an accurate way to test the alternator? That's where I am getting 12V. The FLAPS guy said if I'm getting 12V there then the rest doesn't matter.
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MarkWard
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PostPosted: Mon Oct 08, 2018 11:15 am    Post subject: Re: which new alternator (90 or 65 amp) ? Reply with quote

You need to verify the alternator light is functioning as the other Mark described. Without the OXS and Alternator light coming on with the key, the Alternator has a problem "exciting" to start charging. The main difference between a generator and alternator is the generator charges when it is turning. The alternator, must be excited into charging.
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bobhill8
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PostPosted: Wed Oct 10, 2018 5:29 pm    Post subject: Re: which new alternator (90 or 65 amp) OR is alt fine? Reply with quote

Hey Mark y Mark, I've had a chance to mess around some more. When I start, the battery light on the cluster does not light up at all. The battery stays at 12.0 even after I give it gas to "excite" the alternator. If I turn lights/blower, etc on, it drops to 11 or even 10.7. The engine itself is running fine, but the battery is clearly not getting charged. So what is it that tells the alternator to get to work, and sends the signal to the cluster battery light? Feel free to send me to the Bentley to do my homework. Thanks again, Bob

EDIT: More details. I have the Gowesty alt wiring upgrade kit installed. Should I be studying a wiring diagram at this point and focusing on grounds, or is there another part in the system that I am missing?

BONUS EDIT: I just completed doing the master cylinder and had the instrument cluster out. Could I have messed up something in there?
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Wildthings
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PostPosted: Wed Oct 10, 2018 7:53 pm    Post subject: Re: which new alternator (90 or 65 amp) OR is alt OK? Reply with quote

With the engine running, momentarily short between the B+ terminal and the D+ terminal. If the alternator is okay this should excite the alternator and the voltage should pick up quickly. You should not get much of a spark when you do this, but be wary anyway, a tap is all you should need.
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PostPosted: Thu Oct 11, 2018 1:56 am    Post subject: Re: which new alternator (90 or 65 amp) ? Reply with quote

bobhill8 wrote:
Can you confirm that putting the positive of the multimeter on the post of the alternator directly and the black to ground is an accurate way to test the alternator?


I usually just measure across the battery terminals. With the engine off you should get 12V+ and, with the engine running and if the alternator's "doing it's thing" you should get 13V+

PS: If you do find a 90A alternator that bolts straight on, can you let us know? Coz, it's an upgrade I'm thinking of doing myself at some stage.
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MarkWard
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PostPosted: Thu Oct 11, 2018 5:10 am    Post subject: Re: which new alternator (90 or 65 amp) OR is alt OK? Reply with quote

Key on, small D+ wire at alt disconnected, touch wire to ground and alternator light should light. Report back.
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bobhill8
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PostPosted: Thu Oct 11, 2018 4:07 pm    Post subject: Re: which new alternator (90 or 65 amp) OR is alt OK? Reply with quote

OK, did Mark's test. Key on, oil light on, annoying door sound on. Touch disconnected D+ wire to good ground (another battery negative post). Battery light does NOT come on. Ready for the next step, but am headed to the mtns til Sat afternoon, (without my van-grrrrr). Thanks for the ideas.
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MarkWard
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PostPosted: Thu Oct 11, 2018 6:10 pm    Post subject: Re: which new alternator (90 or 65 amp) OR is alt OK? Reply with quote

Next step, I believe key on same wire disconnected you should have battery voltage. Report back.
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bobhill8
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PostPosted: Fri Oct 12, 2018 5:51 pm    Post subject: Re: which new alternator (90 or 65 amp) OR is alt OK? Reply with quote

Mark, Back early. Test completed. Did NOT get battery voltage. Got 0.00

D+ wire disconnected. Key on. Red lead of multimeter on wire, black lead on good ground. Nothing at all. Battery voltage is a solid 12.8
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bobhill8
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PostPosted: Wed Oct 17, 2018 5:14 pm    Post subject: Re: New alternator (90 or 65 amp) OR is alt ok? SOLVED Reply with quote

Finally solved the "bad alternator" situation. Of course the alternator was fine. As I mentioned at one point, I had just finished doing the master cylinder and had the instrument cluster out. As folks led me through the wiring, I kept thinking that it was an unlikely coincidence. Sure enough, when I finally got around to taking the instrument cluster back out, I saw that I had reinstalled the cluster wiring connector upside down and there was no contact. One simple mistake (50/50 shot) and that held me up for a couple of weeks as I chased wires that were fine. Once I put it back together the right way, the battery light came on, then shut off. Then the alternator kicked in and the battery V shot up to 13.9 and life was good. Well not exactly - now my gas gauge doesn't work! Thanks to Mark Ward and the others who kindly weighed in on the problem.
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bobhill8
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PostPosted: Mon Oct 29, 2018 6:15 pm    Post subject: Re: New alternator (90 or 65 amp) OR is alt ok? SOLVED Reply with quote

One last detail. I was able to get the fuel gauge fixed. I took the instrument cluster back out and took the black connector cover off the blue foil where it connects to the wiring bundle white connector. I could see where some of the copper tabs had been bent back when I put the white connector on backwards earlier. I carefully flattened them back down and put it back together. Not perfect, but good enough so that I now have a fuel gauge again! Until I can afford foil replacement, this will do.
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oceanair
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PostPosted: Mon Oct 29, 2018 6:43 pm    Post subject: Re: New alternator (90 or 65 amp) OR is alt ok? SOLVED Reply with quote

Forget the blue -- go with the Vanagon.org kit and never look back!
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bobhill8
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PostPosted: Thu Nov 01, 2018 4:23 pm    Post subject: Re: New alternator (90 or 65 amp) OR is alt ok? SOLVED Reply with quote

Hey Oceanair, I know, the blue foil should go, but I just bought all new shocks. Gonna have to wait. Saw that you used to have a yellow 71 square. This is my other VW:

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