'41 MB Electrical problems

After sitting for a bit, I planned to take my MB out for a Halloween drive. The day before I drove it to the gas station and it started with no complaints other then my siren sounded weak, so I put it back on my 4A charger maintainer. That day, it started up with no problem, drove it a little ways, started it again and drove home. When I tried to start it again, I had no electrical. No headlights, siren, or starter. When I pressed the starter button I noticed my gauges slowly dying, but would return to their position when I took my foot off. Any ideas here?

Weak battery or corroded battery connections or both. If a 6 volt sits for a while without a charge it won't hold a quick charge. At least that's how my ' 44 GPW is. Check the water level and give it a long charge on a shop charger and check it with a hydrometer .

6 or 12 volt? Bad ground or dead battery

First, I'd load test the battery and see what it says. If it's low, then trickle charge it until it's fully charged.

Then load test it again. Should hold a load for 10 seconds without falling below the threshold.

If all that's good, then I'd make sure the battery connections are all clean, corrosion free and tight. As voltage goes down, amperage goes up so on our elderly 6V systems, everything has to be ship shape.

Let's see some pics of your MB!

So weird thing. I charged the 6v battery overnight tried it this morning and still no joy. I checked all the grounds and everything looked good, but no fire. So I decided to disconnect the battery to clean the terminals. The positive terminal was tight so in the process of untightening it I accidentally tightened it about a quarter turn. Like magic my headlights turned on. I hopped in and it started on the first crank. I can't explain it but I'm not looking that horse in the mouth. Thanks for the responses. I'll post some pictures when the weather clears.

Another thing, I noticed my ammeter is reading zero which would mean the battery is discharging if the gauge is working which I don't totally trust. What is the protocol for testing the output of my generator?

With a decent amount of rpm's you should see about 8v at the battery if it's charging.

Hmm...I put my multimeter on it. Shows 6.46 across the battery when off, and 6.76 with the engine idling at a decent RPM. So I'm guessing I have a bit of an issue here.

Edit: Scratch that. Just tried at a higher rpm than before and getting 7.14v

Where in Texas are you?

McAllen

Generators have a "coming in " speed, where they make proper charging voltage. If one drives the vehicle around in parades or an occasional run around the block, they'll find the battery is often going flat.

If you have a known good ammeter you'll note that the needle will point slightly toward the "-" side of the gauge when at a slow (hot) idle, moving toward the center to slightly charging (+) as engine RPM increases, before finally stabilizing.

Corrosion at the terminal/block junction can be warded off with a touch of copper/nickle based anti-seize, and coating the connected terminals with a bit of vaselene, silicone grease or a smear of GAA.

As long as you keep the inside of the battery terminals clean (clean them with emery paper) and make sure everything is tight..you will be good to go all the time (as long as the battery is good). When the ameter rests towards neutral that only shows a nicely charge battery state.

I have gotten in the habit recently of keeping it connected to my maintainer just to keep the battery charged. I spoke to a mechanic friend, he said the quickest way to determine a generator's current state is to remove a battery terminal with the engine running. If the engine dies the generator is faulty.

GPWWLA said:

I have gotten in the habit recently of keeping it connected to my maintainer just to keep the battery charged. I spoke to a mechanic friend, he said the quickest way to determine a generator's current state is to remove a battery terminal with the engine running. If the engine dies the generator is faulty.

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Never disconnect battery on running vehicle with a generator.
Good way to blow up your electrical system!!

Mechanical voltage regulators work on points opening and closing. The battery stabilizes the system, holding the voltage constant. Without the battery, there will be voltage spikes.
If the points on the voltage regulator are sticking, which often happens when the regulator is ancient, or points are pitted, voltage spikes can reach full generator output - typically around 30 volts.

Guess what that does to anything that is powered up.

I hadn't tried it, just repeating what I had heard. Thanks though

Have you polarized your generator to make sure it's charging?

+1 That is vital.

GPWWLA said:

Hmm...I put my multimeter on it. Shows 6.46 across the battery when off, and 6.76 with the engine idling at a decent RPM. So I'm guessing I have a bit of an issue here.

Edit: Scratch that. Just tried at a higher rpm than before and getting 7.14v

Click to expand...

Sounds like your charging system is working just fine then. Go for a nice 30 mile drive for a good charge.
Remember that battery cables can also have dirty connections at the starter and ground ends, not just at the battery. With a 6-Volt system, clean connections are especially important.