Wiring alternator

[fillpoke]

Once again I need the help of the good people on here. I have a 1972 Beetle 1303s. I've just put in a new (to me) engine which is fitted with an alternator. My old engine had a generator. My problem is that I don't know how I should alter the wiring. Presumably I should do away with the old regulator altogether? Also which wires go where on the alternator? The photo shows my alternator terminals. Thanks for any help, Dave

[ashman40]

To use that alternator you will need an external voltage regular used in the ‘74 Beetle. Somewhere in the ‘74 model year VW switched from generators to alternators. Both charging systems used an external VR but generator VRs are incompatible with alternators so you need to find a compatible “alternator VR”.
Three different styles of alternator VRs are commonly seen on Beetles and some have even reported success using a Ford alternator VR to regulate the alternator output. Here are some pics to help you ID the alternator VRs.

If you can’t find them used you can still buy them new from your FLAPS. Just be sure to have them look up the VR for a ‘74 Beetle with an alternator.

Here’s a pic from Speedy Jim’s site showing how to wire the VR to the 3 prongs on the alternator.

Some alternator VRs had 3 wires, others 4 wires. But the VW alternator only connected to 3 wires from the VR. The 4th wire was for an indicator lamp not used on the Beetle.
Note in the above diagram that the blue #61 wire from the GEN lamp is spliced into the red D+ wire at the VR. The GEN lamp initially provides 12v+ to the D+ wire until the alternator begins charging, at which point the alternator takes over responsibility for providing power to the VR D+. This is a key point with alternators... without the voltage from the GEN lamp (before the engine starts) to "tickle" the charging system to get it charging the alternator spins but does nothing. So even a blown GEN lamp or a loose GEN lamp wire will prevent a working alternator from charging the battery.


Lastly, unlike the generator VR the heavy gauge red wire coming off the alternator’s B+ stud does not connect to the alternator VR. Neither does the heavy gauge wires previously connect to the B+ terminal of the generator VR. In the first pic above you see a large white rectangular wire junction. This replaces the B+ terminal of the generator VR and where all three red wires come together. At this 4-way junction the B+ wire of the alternator, the red wire from the battery positive (+) terminal and the red #30 wire that runs to the front of the car all come together. This allows the alternator to recharge the battery and for either the battery or alternator to power the car electronics via the #30 wire to the front of the car.


PS, while the original VR was installed under the left rear seat there is no reason you can’t install the VR in the engine compartment. Ok, there are a few… the engine compartment is exposed to more heat, moisture and dust than below the rear seat, but I’ve seen VRs live a long life in the engine compartment if placed off to the side like against the firewall or on the fan shroud. This is relevant because you will need 3 small gauge wires running between the alternator and the VR. The generator VR only used 2 small gauge wires. This means you need to run at least one additional wire from the engine compartment into the rear seat area to install the alternator VR there. If you install the VR in the engine compartment you just need to create a new 3wire harness a few feet long to run between the alternator and the VR. The blue #61 wire under the rear seat can be spliced into the existing green wire to extend it into the engine compartment and the end of that wire can be spliced into the red D+ wire at the VR located in the engine compartment to complete the wiring.
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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!}

[fillpoke]

Thanks very much for your comprehensive reply Ashman, it's been a great help.

[Glenn]

If the generator on the old engine is good... i'd just move it to the new engine.

Are you 110% sure the alternator works? If it doesn't any replacement with have an internal regulator.
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Glenn
74 Beetle Specs | 74 Beetle Restoration | 2180cc Engine
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