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Sun Dec 31, 2023 12:38 pm

I've recently run into some issues with my battery, seemingly out of nowhere! Over the summer, I was daily driving my bus, it started with no problem every time, cranked strong, and ran great! Then, in late August, I was driving my bus to storage (I'm a college student and don't have storage at my own place, so I store my bus about 35 miles away in a friend's garage), for the first 32 miles, it ran great, as usual, then I pulled into a gas station to top off the tank, and when I tried to start the vehicle after filling up, it was DEAD, like couldn't even crank. A nice guy came by and jumped me, only took about 30 seconds on the cables and it started right up. I drove the rest of the way to storage, turned it off, and tried to start the engine again (just to test) and it was dead again. It still starts on a jump, but the battery doesn't seem to be charging.

Now that the semester is over, I got back to my bus, and the problem persists. After charging the battery for a while, I got it to start and immediately noticed some issues. Every plug on the voltage regulator read between 10-40 millivolts, and when pulled from the battery, the charging lead only read about 242 millivolts. And when running, the battery is at ~5 volts :shock: When not running, the battery reads 7.5 volts. The engine is now dying because the battery can't power the electric fuel pump I use (my Webber single carb is getting 0.5psi fuel pressure)

TLDR: I thought that I might just need a new voltage regulator, but am I wrong in thinking that the alternator should still be putting out voltage even if the regulator is bad? Should I just try a new regulator and a new battery?

P.S. I installed a new wiring harness about 2 years ago and until now have had no issues with electronics.

Sun Dec 31, 2023 12:52 pm

my first thought is dead battery (simplest solution). but, there are folks with more electrical knowledge than i possess.

have you tested the voltage output from the alternator? should be 14 volts.

not sure the year of your bus matters, but you might post it in case.

Sun Dec 31, 2023 1:10 pm

you have an electrical problem that cannot be solved by just pulling wires and seeing what they are doing. In fact, that can make things go from bad to worse.

It could be anything from a broken wire to a bad alternator, to a bad regulator or battery. Even a slipping belt. Grounds have to be checked, posts and cables cleaned.

Whatever you do is going to cost some time and money to fix if you pay someone. Shop rates out here are about $175 - $200 an hour. My suggestion is find someone who understands charging systems and see if they can help you out of the kindness of their heart. IMHO, doing this over the Internet while attending college is unlikely to be successful. Electrons are unforgiving. Throwing parts at it is unlikely to be successful as well.

Also, if you decide to tackle this yourself, better ask yourself how much time you can throw at it. If you are lucky and it is just a loose wire you find 5 minutes in that is super. If it is a failed alternator and you have to pull the engine and shroud, could take considerable more time.

Good luck.

Sun Dec 31, 2023 1:54 pm

Check the block that plugs into the base of the V.R. The individual wires can end up working away from the actual contacts to the regulator's internal circuits. I guess that is so due to the harness plugging in from below.?
Had an old '74 bus, ended up making sure each wire in the block was seated to each contact blade, they were that loose in the plastic /nylon? block. lol.
The brushes inside the alternator can also wear to the point you get near no contact on the slip rings. : ( & low voltage. / warning light on the dash.

Sun Dec 31, 2023 2:25 pm

Hi All, thank you for the feedback. It's a '74 bay window, I rebuilt the engine about 3 years ago, including having the alternator completely rebuilt and upgraded to 70 amp. The battery is about 2.5 years old and until August, was always healthy and happy. Belt tension is good, deflects ~0.5 inch.

I am home on an internship for a while, so I should be able to dedicate enough time to solve this myself. (And I have no money because of the aforementioned college, so I can't pay someone to fix it for me :lol: )

The VR Wire connections are all solid, checked those.

The alternator output (big red wire going from alternator to + terminal on batt), which should be 14 volts when the engine is idling, read 242 millivolts (basically zero volts), which confused me. The belt wasn't slipping, so even if the VR was bad, wouldn't it still output voltage?

Sun Dec 31, 2023 3:32 pm

https://www.thesamba.com/vw/forum/search.php?searc..._chars=200

Read a few of these topics carefully, you'll see posts by a guy named Telford Dorr, when he describes tests do them on yours if it's discussing a similar symptom.

Sun Dec 31, 2023 4:21 pm

Quote: The alternator output (big red wire going from alternator to + terminal on batt),

I would check my meter first with a known good AA alkaline battery. It should be 1.5V. If you are reading between batter POSTS you should have close to 12V. If you then read between chassis ground and the +Battery post you should have about the same voltage.

BEWARE that battery cable colors mean nothing. Go by the + / - on the battery. Very often the cable colors may be reversed or both red, or both black which will result in all sorts of damage if someone assumes black and red mean something.

Sun Dec 31, 2023 10:15 pm

Hodence wrote: The alternator output (big red wire going from alternator to + terminal on batt), which should be 14 volts when the engine is idling, read 242 millivolts (basically zero volts), which confused me...
Compare that voltage to what's at the battery + terminal. As they are connected together, they should read the same voltage. If they differ, figure out why:

- dirty/corroded battery terminals.
- corroded aftermarket clamp-on battery terminals. [Don't use these - they're nothing but trouble. Use one-piece cables.]
- bad red wire / terminals between alternator and starter / battery.
- bad butt splice connecting red alternator wire to positive battery cable.
Note: do not use a ring terminal under the battery clamp bolt - too susceptible to corrosion.

To start with, fully charge the battery with an external charger (smart charger preferred). Will simplify further testing.

Post results of red wire test and its resolution. Further testing to follow based on the results.

Mon Jan 01, 2024 4:09 am

I would certainly be afraid at this point that you may have hooked the cables up backwards when you charged the battery. This would take out the diodes in the alternator and give you no charging voltage.

It's also possible that when the alternator was rebuilt, the studs for the diode plate didn't get shortened and eventually contacted the cover causing a dead short thus destroying the alternator.

Mon Jan 01, 2024 11:02 am

I appreciate all the ideas. My multimeter is a good one, but just to be safe I checked it w/ AA and 9V batteries, and it's reading spot on.

I definitely didn't connect the battery charger backward, and even if I did, it's one of the new smart chargers with reverse polarity protection. I fully restored the bus over the past few years, including new positive and negative cables, so I know for a fact which is which and that they're on the correct terminals.

The battery is very dead right now from running the engine without an alternator, but I have it on the charger. Wildthings, is there a way that I can check if the diode in the alternator is shot? I had a professional alternator and starter shop do the rebuild, so I doubt they made a mistake (especially because the bus ran for 2 years with the new alternator), but maybe they made a mistake.

If I pull the alternator and spin it by hand, should the red wire (that butt-splices to the positive terminal) output voltage even when none of the other wires are connected to the voltage regulator?

Mon Jan 01, 2024 11:26 am

The alternator needs voltage from the blue wire coming from the dash to excite it. If there is a problem with this wire and/or the charge warning bulb in the dash cluster the alter will not excite, zip, nada, nothing.

Your rebuilder may not be aware that there was a very minor change in the length of the studs on the diode plate and its possible that the problem would take many miles to show up. On my '77 nearly twenty years ago it took several hundred miles to appear and then suddenly POP the alternator was history. Had I repainted the rear cover for the alternator or the cover been slightly warped it could have taken much longer to show up.

Mon Jan 01, 2024 11:42 am

Wildthings wrote: Your rebuilder may not be aware that there was a very minor change in the length of the studs on the diode plate and it’s possible that the problem would take many miles to show up. On my '77 nearly twenty years ago it took several hundred miles to appear and then suddenly POP the alternator was history. Had I repainted the rear cover for the alternator or the cover been slightly warped it could have taken much longer to show up.

mike, i know that’s true for 55-amp alternators. he was a 70-amper. they don’t have the same problem, as no backing plate, right?

Mon Jan 01, 2024 11:59 am

dodger tom wrote: Wildthings wrote: Your rebuilder may not be aware that there was a very minor change in the length of the studs on the diode plate and it’s possible that the problem would take many miles to show up. On my '77 nearly twenty years ago it took several hundred miles to appear and then suddenly POP the alternator was history. Had I repainted the rear cover for the alternator or the cover been slightly warped it could have taken much longer to show up.

mike, i know that’s true for 55-amp alternators. he was a 70-amper. they don’t have the same problem, as no backing plate, right?
Maybe, but the OP says" alternator completely rebuilt and upgraded to 70 amp.", that could mean 70lbs of shit stuffed into a 55lb sack.

Mon Jan 01, 2024 12:41 pm

busdaddy wrote: dodger tom wrote: Wildthings wrote: Your rebuilder may not be aware that there was a very minor change in the length of the studs on the diode plate and it’s possible that the problem would take many miles to show up. On my '77 nearly twenty years ago it took several hundred miles to appear and then suddenly POP the alternator was history. Had I repainted the rear cover for the alternator or the cover been slightly warped it could have taken much longer to show up.

mike, i know that’s true for 55-amp alternators. he was a 70-amper. they don’t have the same problem, as no backing plate, right?
Maybe, but the OP says" alternator completely rebuilt and upgraded to 70 amp.", that could mean 70lbs of shit stuffed into a 55lb sack.
hadn’t thought of that. i stand corrected.

Mon Jan 01, 2024 12:41 pm

I'll look into the blue wire, honestly, I don't know if my dash battery bulb was in and working. I assume it was bc once again, haven't had any charging issues in 2 years. Maybe the bulb just burnt out.

And as far as the alternator, yeah, 70 lbs of sh*t stuffed into a 55 lb sack. It has a backing plate, although the plate was repainted when it was rebuilt. Up until now, it's seemed great, but now I'm curious if my "budget" solution to buying a 70 amp alternator was a bad idea.

Mon Jan 01, 2024 4:53 pm

all alternators need to be excited to work. They do not carry a residual magnetic charge like a generator. No voltage to that blue wire and no excitement, no output. A FI bus needs around 10V just to run. Carb bus only needs a small spark.

Tue Jan 02, 2024 9:49 am

I'll look into the blue wire voltage. As I said, all terminals on the voltage regulator were basically zero.

What voltage should the exciter (blue) wire be at?

By the way, my bus is carbureted and has run on as little as ~5 volts (bc I was running it without charging the battery and discharged it) and I believe the spark was still fine, I have an inline fuel pressure gauge and it was reading 0.5 psi, so I think that the low voltage just couldn't run the electric fuel pump

Tue Jan 02, 2024 1:25 pm

Hodence wrote: I'll look into the blue wire voltage. As I said, all terminals on the voltage regulator were basically zero.

What voltage should the exciter (blue) wire be at?

By the way, my bus is carbureted and has run on as little as ~5 volts (bc I was running it without charging the battery and discharged it) and I believe the spark was still fine, I have an inline fuel pressure gauge and it was reading 0.5 psi, so I think that the low voltage just couldn't run the electric fuel pump

The blue wire should have close to battery voltage when the key is in the "ON" position (engine not running and the blue wire not hooked up to the regulator), and if grounded out it should make the charge warning light come on. The light should also be on when both the alternator and regulator are fully connected and the key is "ON".

Wed Jan 03, 2024 12:36 am

I had trouble with the blue wire loose at the VR plug.

Wed Jan 03, 2024 2:51 am

If you let that battery sit dead, like under 12 volts for any length of time ( weeks) it will be dead and need replacement. A car that sits needs a trickle charger to keep electrics happy. Semester breaks are too long to let a car sit.