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jplava
Samba Member
Joined: August 07, 2025
Posts: 2
Location: PA
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 Posted: Fri Aug 08, 2025 7:32 am Post subject: Terminals reversed on battery, what now? |
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I bought a 72 Beetle that was sitting for 5 years. The people said they put in a new battery. They said it would crank but it still wouldn't start. I brought it home and put a charger on the battery and noticed the battery was in backwards with positive and negative reversed. I got them put on correctly and now the battery light is on when the key is off and the ceramic unit on top of the generator is hot. Is my generator ruined or could something else, (like the voltage regulator) be ruined and causing the generator to be hot?
I haven't tried to start it yet because it has no gas in it. But it does crank over
Any suggestions are appreciated
Last edited by jplava on Fri Aug 08, 2025 8:54 am; edited 1 time in total |
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runamoc 
Samba Member
Joined: June 19, 2006
Posts: 6212
Location: 37.5N 77.1W
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| Posted: Fri Aug 08, 2025 8:19 am Post subject: Re: Terminals reversed on battery, what now? |
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| battery light is on when the key is off |
The contacts on the large wire coil in the Voltage Regulator is either stuck or welded together.
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Daily driver: '69 Baja owned 45 yrs - Plan B: '72 Ghia
Yard Art: 2 Sandrails
Outback: '69 Ghia - '68,'69,'70,'72 Beetle - '84 Scirocco, GTI - Pair of '02 Golfs- '80 Rabbit Diesel
VW Wiring = It's just wires |
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rg65
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Joined: January 24, 2025
Posts: 11
Location: New Mexico
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| Posted: Fri Aug 08, 2025 8:54 am Post subject: Re: Terminals reversed on battery, what now? |
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| Bummer DC circuits do not like being reversed. Good chance the voltage regulator is damaged. If your fuel injected may have done damage to those circuits as well and If the radio was turned on it may also be toast. Check the fuses they may have done their job and and protected the circuits. The light being on does suggest something in the charging system is not happy. |
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runamoc
Samba Member
Joined: June 19, 2006
Posts: 6212
Location: 37.5N 77.1W
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| Posted: Fri Aug 08, 2025 9:02 am Post subject: Re: Terminals reversed on battery, what now? |
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| Quote: |
| fuses they may have done their job and and protected the circuits |
Fuses only protect the wires, not what's hook up to the wires
_________________
Daily driver: '69 Baja owned 45 yrs - Plan B: '72 Ghia
Yard Art: 2 Sandrails
Outback: '69 Ghia - '68,'69,'70,'72 Beetle - '84 Scirocco, GTI - Pair of '02 Golfs- '80 Rabbit Diesel
VW Wiring = It's just wires |
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busdaddy
Samba Member
Joined: February 12, 2004
Posts: 52885
Location: Surrey B.C. Canada, but thinking of Ukraine
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| Posted: Fri Aug 08, 2025 9:34 am Post subject: Re: Terminals reversed on battery, what now? |
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Welcome!
| jplava wrote: |
| ........... and the ceramic unit on top of the generator is hot. .............. |
Does it look like this?:
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ashman40
Samba Member
Joined: February 16, 2007
Posts: 16635
Location: North Florida, USA
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| Posted: Fri Aug 08, 2025 1:17 pm Post subject: Re: Terminals reversed on battery, what now? |
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| jplava wrote: |
| I bought a 72 Beetle that was sitting for 5 years. The people said they put in a new battery. They said it would crank but it still wouldn't start. I brought it home and put a charger on the battery and noticed the battery was in backwards with positive and negative reversed. |
Just to be clear... the positive post (+) was connected to the cable that runs to the chassis and the negative post (-) was connected to the cable that runs thru the floor pan to the starter. Is this what you are describing?
If you had to guess, how long was it connected this way?
The good thing for you is that early Beetles like your '72 had few devices that were polarity sensitive. The VR/alternator/generator is one. Maybe if you installed a modern digital stereo it too might have been damaged. But most of the other electronics in the Beetle don't really care which direction the current flow. They may not work, but they are likely not damaged permanently.
| jplava wrote: |
| I got them put on correctly and now the battery light is on when the key is off and the ceramic unit on top of the generator is hot. Is my generator ruined or could something else, (like the voltage regulator) be ruined and causing the generator to be hot? |
I was pondering what you could mean by "ceramic unit" until I saw busdaddy's post above.
| busdaddy wrote: |
Does it look like this?:
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The pic posted is of an early alternator with the VR mounted externally to the body of the alternator. There is another model (AL-7 which had 4-wires and placed the VR remotely (under the rear seat). Finally, there was the later model alternators (AL-82) which used only 2-wires and had the VR inside the alternator.
Are you running an alternator or the earlier generator? Post a pic.
If you have a generator, read Speedy Jim's page on generator troubleshooting:
https://speedyjim.net/htm/gen.htm
If you have an alternator the above Speedy Jim page will not help you at all.
If you have the AL-78 4-wire alternator you can do some troubleshooting to test the alternator separately from the VR. If the VR is failed it is easy to replace. If the alternator is internally damaged you pretty much need to replace it or get it rebuilt.
| jplava wrote: |
| I haven't tried to start it yet because it has no gas in it. But it does crank over |
So, with the battery connected correctly, your starter cranks the engine CW when you turn the key? At least this confirms the starter was not damaged.
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AshMan40
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'67 Beetle #1 {project car that never made it to the road  }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!} |
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Cusser
Samba Member
Joined: October 02, 2006
Posts: 33161
Location: Hot Arizona
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| Posted: Fri Aug 08, 2025 4:22 pm Post subject: Re: Terminals reversed on battery, what now? |
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| jplava wrote: |
| I bought a 72 Beetle that was sitting for 5 years. The people said they put in a new battery. They said it would crank but it still wouldn't start. I .... noticed the battery was in backwards with positive and negative reversed. |
Some doofi (doofuses?) should be prevented from touching a vehicle or tool !
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1970 VW (owned since 1972) and 1971 VW Convertible (owned since 1976), second owner of each. The '71 now has the 1835 engine, swapped from the '70. Second owner of each. 1988 Mazda B2200 truck, 1998 Frontier, 2014 Yukon, 2004 Frontier King Cab. All manual transmission except for the Yukon. http://www.thesamba.com/vw/forum/album_page.php?pic_id=335294 http://www.thesamba.com/vw/forum/album_page.php?pic_id=335297 |
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jplava
Samba Member
Joined: August 07, 2025
Posts: 2
Location: PA
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| Posted: Fri Aug 08, 2025 6:37 pm Post subject: Re: Terminals reversed on battery, what now? |
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Yes Ashman40, that is exactly what it looks like. I guess I'll get a new alternator and a new stereo too. It doesn't work either. It seems it was hooked up incorrectly for five years or at least until the battery went dead.
Thanks guys for all the input. Without your help I would be guessing my next step |
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