TheSamba.com :: View topic

Wed Oct 21, 2009 6:57 pm

does a 1972 mexi bug have a ballast resistor in the ignition system?

Wed Oct 21, 2009 7:39 pm

From the factory no air cooled beetle has a ballast resistor from the factory, the coils had internal resistors. Must be a present from a previous owner.

Wed Jul 03, 2013 8:28 am

Sorry for bringing this thread from the dead, but I needed to get a new coil for my '74 super & the catalog asked if the car had an external resistor or not. That got me confused; because I didn't see a typical resistor- so I ended up buying a non-external resistor coil. Was I correct in this? Thank you!
Ken

Wed Jul 03, 2013 8:42 am

The stock Beetle ignition coil had a 3~4-ohm resistor built into the coil. If you measured the resistance between the #15 (+) and the #1 (-) terminals you should get a reading in the 3~4-ohm range.
Your replacement coil should have the same resistance. If it doesn't, you could add an old style external ballast resistor to raise the resistance into the expected range.

If you fail to have the correct resistance between the 12v source and the ignition coil you will burn the points as too much current will flow through the points.

Wed Jul 03, 2013 8:53 am

I think the resistance you measure is likely just the coil resistance, i.e. the resistance of the wire itself.

Mon Sep 30, 2013 7:26 am

I am in a situation where I have lent my coil to another person so he can confirm the coil was the problem. His Thing would run for about 8 miles and then the ignition would stop (no spark).

I lent him my coil and while installing it, I found that his coil required an external resistor.

I found one at O Reilly that I can use with his coil on my car while he is still testing and acquiring an internal resistor coil.

The part number that works is RU6 from BWD engine management technology. I just zip tied the resistor and coil as this is a temporary solution.

The black wire is from the ignition.... Terminal #15 which would typically go to the positive side of the coil. The Green wire is going to terminal #1 which still is the negative side of the coil. The white wire jumps the output of the resistor to terminal #15 on the coil.

As a special note, disconnect the backup lights as they will draw too much current from the ignition when you put the car in reverse and make the car run poorly. Or, you could just attach it to the black wire in this example (catch the full current before it is reduced by the resistor.)

Tue Oct 01, 2013 9:06 am

I couldn't find a spec for that RU6 ballast resistor. Its not clear how many ohms of resistance the resistor adds.

Because the resistor is wired in series the resistance adds up. If the internal resistance of the coil is, for example, 1.5-ohms. Then you will need at least another 1.5-ohms of additional resistance from the ballast resistor to bring you up to 3.0-ohms.

If you search Summit Racing you can find a collection of ballast resistors rated at different resistances.
http://www.summitracing.com/int/search/part-type/b...=Ascending

Tue Aug 20, 2024 10:50 am

Returning to this discussion 11 years later.... A ballast resistor and a bunch of other questionable wiring were added at some point (coil to starter motor) to my 73 Superbeetle. A ballast resistor was essential for the Triumph Spitfire I had before this, so I thought little of it until I replaced the starter and noticed that coil-to-starter wire went through the resistor. My question about the need for a ballast resistor brought me here. I had read about that being done to give more power to the starter, but not with the VW. And it seems the ballast resistor is not necessary. Both the wire and the resistor are gone.

I am posting because of a related problem that was inspired by this thread: The car stalled when I put it in reverse. It drove me crazy as it continued after I had replaced all of the wires. I unattached each of the reverse lights to find if the problem was there. It would indicate the right. Then not. Then the left. Then not. What I noticed was that the problem stopped after the engine warmed up. At first, I assumed it just didn't stall as it might when cold. But then I noticed that the reverse wires shared the same terminal with the ignition wire, while the choke was alone. Then stevewp mentioned the reverse lights drawing a lot of power. I wondered if the warmed up engine needed less from the coil, or if the warmed up coil gave more, or.... Doesn't matter. The ignition is on its own and the reverse lights share with the choke. All is well.

Tue Aug 20, 2024 11:51 am

I would not depend on the electrical performance standards of a British sports car... the Prince of Darkness has a wide reach and power (or lack of it)...

Neither the choke nor the backup lights should draw so much current that you have ignition problems. Either those circuits or the ignition circuit itself must have issues, and those should be resolved, not by re-engineering a system that worked fine for 20 million vehicles.

Some American cars used a coil resistor as compensation for significant voltage drop when cranking, and the resistor was bypassed during cranking. Maybe those British cars had some variation of this?

Not needed for a properly wired and functioning Beetle electrical system.

Tue Aug 20, 2024 1:30 pm

KTPhil wrote: Some American cars used a coil resistor as compensation for significant voltage drop when cranking, and the resistor was bypassed during cranking. Maybe those British cars had some variation of this?
Agreed. Some '50s/'60s ACVW may have run a wire from the extra terminal on the starter solenoid to the ignition coil to BYPASS the ballast resistor and give the ignition a hotter spark while the starter was cranking. But a '73 Beetle would not have come with such wiring.

The unused male terminal in the above pic is wired to the large threaded stud closest to the starter motor. When the motor is energized the small terminal is also powered by the battery. When you run a wire from this unused terminal to the ignition coil #15 it will provide direct battery current to the starter. This arrangement only really makes sense if running an external ballast resistor. The common internal ballast resistor built into the OE ignition coils benefit little from such bypass wiring. If there is actually a resistor in the wire running from the starter solenoid to the ignition coil you completely defeat the purpose.

Are you sure of the wiring you have described? Normally, there is no wire running between the ignition coil and the starter. Can you post pics?

On your problem with the reverse lights....
There should normally be a black wire with an inline fuse connected from the ignition coil #15 (+) terminal and the reverse light switch at the front end of the transmission. If you incorrectly connect this black wire to the #1 (-) terminal on the ignition coil it will short the ignition coil primary winding to ground every time you shift into reverse. This will immediately prevent the ignition coil from firing sparks and kill the engine. This used to be a common prank.
Check the wiring at your ignition coil. There should only be one wire connected to the coil #1 (-) terminal... it is the wiring croming from the points/condenser in the distributor. With the exception of the diagnostic and tachometer wires, nothing else should connect to the #1 (-) terminal on the coil.
On the other side of the coil, MANY things will connect to the #15 (+) terminal of the coil. These devices will draw power from the #15 terminal.

It is possible the reverse lights are drawing too much power away from the ignition coil. This is typically caused by old wiring. As wires age they build up corrosion and dirt at the wire junctions. This increases the resistance in the wire paths. More resistance means less current will make it to the end of the circuit. All the devices connected to the #15 terminal of the ignition coil draws power from the junction. The available current comes from the single black #15 wire coming from the fuse box/ignition switch. If this wire is old and its many connections are oxidized it means much less current is making its way to the ignition coil. Everything connected to the ignition coil #15 is drawing current away from the coil itself.

Test the voltage that makes it to the #15 terminal. It should be within 0.5v of the battery voltage (12.6v). If it is much less than this it means old wires or it means a weak battery.

Tue Aug 20, 2024 2:51 pm

As an FYI, that "energized only when cranking" male tab is also used by the FI to enable a cold start valve on some D-Jet models.