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Tbrier100
Samba Member
Joined: November 11, 2024
Posts: 24
Location: Florida
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 Posted: Thu Jul 10, 2025 4:24 pm Post subject: Battery light comes in intermittently |
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| I have a 1979 vw bus, and I have a new 70 amp alternator from bus depot, new harness and new regulator. my battery light comes on randomly and I drop back to 12.5 volts, then ill drive a bit and it will start working again. I took the alternator out and got it tested, they said it was good. I just don't know what's going on. |
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lil-jinx
Samba Member
Joined: August 14, 2013
Posts: 1577
Location: New Brunswick,Canada
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Tbrier100
Samba Member
Joined: November 11, 2024
Posts: 24
Location: Florida
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| Posted: Thu Jul 10, 2025 4:36 pm Post subject: Re: Battery light comes in intermittently |
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| lil-jinx wrote: |
| why did you install the new parts? |
New engine didn’t know how the alternator was. I also wanted a 70 amp so I put that in and it ran good for a bit then went. The light came on so that I tried a new regulator and it worked for a bit. Then the light came on again.
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timvw7476
Samba Member
Joined: June 03, 2013
Posts: 2490
Location: seattle
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| Posted: Thu Jul 10, 2025 5:04 pm Post subject: Re: Battery light comes in intermittently |
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| I would go back to the old regulator first as the first step. Much easier to do than any other troubleshooting step. Quick n' Dirty. |
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mikedjames
Samba Member
Joined: July 02, 2012
Posts: 3320
Location: Hamble, Hampshire, UK
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| Posted: Fri Jul 11, 2025 4:43 am Post subject: Re: Battery light comes in intermittently |
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If the alternator uses a modern regulator, these use the 12 volt feed via the warning light as an enable control. After 12 volts appears on the wire for a while, the alternator starts up. If the 12 volts vanishes momentarily, it shuts down and the warning light comes on as it reconnects for about 0.5 to 1 second depending on the regulator. If during that time the 12 volts varnishes, the timer restarts..
A worn ignition switch or a loose warning bulb or a loose spade connector can make this happen, vibration keeps it mostly connected with occasional disconnections, alternator light stays on, maybe flickers a bit, alternator never starts up.
Its different to older simpler regulators , they would work with a loose wire, as once the alternator has started producing voltage, it does not need the presence of the warning light until it stops.
_________________
Ancient vehicles and vessels
1974 VW T2 : Devon Eurovette camper with 1641 DP T1 engine, Progressive carb, full flow oil cooler, EDIS crank timed ignition.
Engine 1: 40k miles (rocker shaft clip fell off), Engine 2: 30k miles (rebuild, dropped valve). Engine 3: a JK Preservation Parts "new" engine, aluminium case: 26k miles: new top end.
Gearbox rebuild 2021 by Bears.
1979 Westerly GK24 24 foot racer/cruiser yacht Forethought of Gosport.
1973 wooden Pacer sailing dinghy |
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Tbrier100
Samba Member
Joined: November 11, 2024
Posts: 24
Location: Florida
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| Posted: Fri Jul 11, 2025 7:48 am Post subject: Re: Battery light comes in intermittently |
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| timvw7476 wrote: |
| I would go back to the old regulator first as the first step. Much easier to do than any other troubleshooting step. Quick n' Dirty. |
I didn't have an original one in there so I ordered another one, it should be here tomorrow. |
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Tbrier100
Samba Member
Joined: November 11, 2024
Posts: 24
Location: Florida
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| Posted: Fri Jul 11, 2025 10:48 am Post subject: Re: Battery light comes in intermittently |
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| mikedjames wrote: |
If the alternator uses a modern regulator, these use the 12 volt feed via the warning light as an enable control. After 12 volts appears on the wire for a while, the alternator starts up. If the 12 volts vanishes momentarily, it shuts down and the warning light comes on as it reconnects for about 0.5 to 1 second depending on the regulator. If during that time the 12 volts varnishes, the timer restarts..
A worn ignition switch or a loose warning bulb or a loose spade connector can make this happen, vibration keeps it mostly connected with occasional disconnections, alternator light stays on, maybe flickers a bit, alternator never starts up.
Its different to older simpler regulators , they would work with a loose wire, as once the alternator has started producing voltage, it does not need the presence of the warning light until it stops. |
so would I not have any voltage at D+ (red/blue wire)? I got someone else's regulator and tried it, same thing went off for a while while driving then the light came on. drove for a bit it went off then came back on |
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Tbrier100
Samba Member
Joined: November 11, 2024
Posts: 24
Location: Florida
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| Posted: Fri Jul 11, 2025 11:04 am Post subject: Re: Battery light comes in intermittently |
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| mikedjames wrote: |
If the alternator uses a modern regulator, these use the 12 volt feed via the warning light as an enable control. After 12 volts appears on the wire for a while, the alternator starts up. If the 12 volts vanishes momentarily, it shuts down and the warning light comes on as it reconnects for about 0.5 to 1 second depending on the regulator. If during that time the 12 volts varnishes, the timer restarts..
A worn ignition switch or a loose warning bulb or a loose spade connector can make this happen, vibration keeps it mostly connected with occasional disconnections, alternator light stays on, maybe flickers a bit, alternator never starts up.
Its different to older simpler regulators , they would work with a loose wire, as once the alternator has started producing voltage, it does not need the presence of the warning light until it stops. |
so I don't have my fan hooked up and have the wires for the fan just hanging out I did cap off the red power one. but there is a blue one that splits from the alternator harness, if that grounds could that cause my problem?
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