Bypass Amp Meter

Boy - it's been years since I had a car with an AMP meter.  They were more accurate it showing charging/dis-charging but took big cables and if you shorted them - could melt wires and start fires!  Maybe someone with more recent/expertise can chime in.  Yeah, they could all be connected together but need to be well insulated/isolated.  I think I would trace wires back to the source and disconnect them (or remove them there).  I'm guessing you'd still need wire that goes from alternator to battery/starter solenoid.  A volt meter just takes small gauge wire.

Thanks so much Wolfgang that's exactly what I am trying to bypass... Thinking a modern lever nut and maybe adding an inline fuse as currently there is no fuse in the connection from the battery to the alt/reg, but not sure of the amp needed on the fuse?

I'd don't like those connectors.  They are used in walls of my current condo and I've had a couple fail.  I can see signs of arcing and the connectors seem to get loose in the wall.  Seems in a car they would jossle around and come loose.  If leaving wires there - I'd use a butt connector securely soldered with several layers of shrink wrap on it (not just electrical tape) and then securely held in place away from frame metal with nylon ty-wraps.

Perfect! Thanks so much Where are you located in Florida?  I live on Amelia Island, currently getting rained out for the Concours De'Elegance....

@LotusEarth at soggy Amelia....

I've just spent the past 40 minutes pouring through the CMC assembly manual and can add to Wolfgang's post.  It looks like the builder used the CMC wiring harness because your wire colors line up with what's in their incredibly poor schematics.

The 10 ga orange wire at terminal "I" goes from the Ammeter to the fuse block to supply power to most of the car.  It should go to terminal #3 or 4 on the fuse block (assuming they used the original VW block).  When disconnected from the ammeter, it should show zero volts.  

Depending on the type of Ammeter, there should be one or two 10 ga (probably Red) wires going to terminal "S".  If you disconnect them, one should be +12 volts all the time and the other may go to zero when loose.

If you have an earlier generator, one (the dead one) typically goes to the generator's voltage regulator B+ terminal.  If you have a modern Alternator then that red wire goes to the big B+ stud on top of the alternator.  That is where the rest of the car gets it's electrical power from.

The other 10 ga red wire goes to the battery terminal at the starter solenoid.  (This is unclear in the CMC manual because there are a few inconsistencies in this section.)  That is how the generator/alternator gets it's charging power into the battery.

There may also be a smaller gauge (like 12 ga or so) wire also connected to the "S" ammeter terminal, and that should go to the headlight "30" terminal to provide power to the lights.  This may not be there in your car if they picked up +12 volts for the lights elsewhere (like at the fuse block).

So, Bottom line, what should you do to eliminate the Ammeter?  

Connect both Red 10 ga wires (along with the may-be-there 12 ga white wire) previously connected to the "S" terminal and the Orange 10 ga wire from the "I" terminal together with a firm, mechanical connection, cover the connection with at least two layers of shrink tube and then tie it off safely so it can't flop around.  That should get your power back to everything else and by-pass the gauge.  Remember that the Red and Orange wires ARE NOT FUSED at this point.  If you wish to have a master fuse in there, it should be at the starter end of the Red wire, it should be around 40 - 50 amps and it should be water-proof.

That's about it.  Don't worry about having a voltmeter rather than an Ammeter.  That does not apply to what you're trying to do.

Good Luck and no sparks....

Haven't seen an ammeter like that in fifty years. "Vintage" describes it pretty well. That little bar that connects the two posts on the back is probably a shunt. Current flows across that but because it has a known resistance the ammeter reads the difference and is designed to convert that difference into amps.........Bruce

Close, but not quite, Bruce….

The horizontal bar across the back is the bracket that holds the gauge into the dash.  Look closely and you can see it trailing off the sides and headed toward the front of the gauge.

The current flows between the “S” and “I” studs at the bottom in the photo.  “I” goes to the fuse block and “S” goes to the alternator/generator and battery.  That puts the gauge in between the battery and everything else to show current flow to and from the battery.

A “shunt-style” ammeter relied on a device (called the shunt) that was a special wire between the generator and battery that had a section with another wire wrapped around it in a coil.  That coil wire sampled the current flowing in the main wire and converted that to a voltage that fed the dash gauge (meter).  This differed from the ammeter in the above posts which has big, beefy wires from the generator and battery going up behind the dash and sampled the current directly (actually by the same method, but the sample coil is inside the gauge can).  This direct-sample method was felt to be less safe than the wire shunt version, which was thought to be safer because far less current had to be brought to the dash from the engine bay.

Either version did a good job of telling the driver what was going on with their electrical system, but few people, these days, probably remember how to read an Ammeter and know what it means, especially as it could swing either way, plus or minus, around the center of the gauge.  

OH Yeah !  Now I see that,  my mistake.  I actually liked the direct read ammeters. They would tell you which way it was flowing and good for trouble shooting.  Yup, the problem is the heavy gauge wires necessary. Especially with 100 amp altenators these days. Thanks Gordon..............Bruce

@Gordon Nichols posted:

@LotusEarth at soggy Amelia....

I've just spent the past 40 minutes pouring through the CMC assembly manual and can add to Wolfgang's post.  It looks like the builder used the CMC wiring harness because your wire colors line up with what's in their incredibly poor schematics.

The 10 ga orange wire at terminal "I" goes from the Ammeter to the fuse block to supply power to most of the car.  It should go to terminal #3 or 4 on the fuse block (assuming they used the original VW block).  When disconnected from the ammeter, it should show zero volts.  

Depending on the type of Ammeter, there should be one or two 10 ga (probably Red) wires going to terminal "S".  If you disconnect them, one should be +12 volts all the time and the other may go to zero when loose.

If you have an earlier generator, one (the dead one) typically goes to the generator's voltage regulator B+ terminal.  If you have a modern Alternator then that red wire goes to the big B+ stud on top of the alternator.  That is where the rest of the car gets it's electrical power from.

The other 10 ga red wire goes to the battery terminal at the starter solenoid.  (This is unclear in the CMC manual because there are a few inconsistencies in this section.)  That is how the generator/alternator gets it's charging power into the battery.

There may also be a smaller gauge (like 12 ga or so) wire also connected to the "S" ammeter terminal, and that should go to the headlight "30" terminal to provide power to the lights.  This may not be there in your car if they picked up +12 volts for the lights elsewhere (like at the fuse block).

So, Bottom line, what should you do to eliminate the Ammeter?  

Connect both Red 10 ga wires (along with the may-be-there 12 ga white wire) previously connected to the "S" terminal and the Orange 10 ga wire from the "I" terminal together with a firm, mechanical connection, cover the connection with at least two layers of shrink tube and then tie it off safely so it can't flop around.  That should get your power back to everything else and by-pass the gauge.  Remember that the Red and Orange wires ARE NOT FUSED at this point.  If you wish to have a master fuse in there, it should be at the starter end of the Red wire, it should be around 40 - 50 amps and it should be water-proof.

That's about it.  Don't worry about having a voltmeter rather than an Ammeter.  That does not apply to what you're trying to do.

Good Luck and no sparks....

Thanks so much for this valuable and appreciated information Gordon I did manage to bypass the amp meter with a really nice junction device I found at Lowe’s. I’ll include a photo for reference… All seems to be working fine now.  Thanks again for the kind advice

@aircooled posted:

OH Yeah !  Now I see that,  my mistake.  I actually liked the direct read ammeters. They would tell you which way it was flowing and good for trouble shooting.  Yup, the problem is the heavy gauge wires necessary. Especially with 100 amp altenators these days. Thanks Gordon..............Bruce

Thanks for the reply Bruce… The amp meter is an interesting device for sure.  

Glad it all worked out for you.  Good luck with the rest of the renovations!

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I was wondering how that all worked and did some sleuthing of my own.

Found a YouTube video by a mechanic who seemed to know his stuff, and he explained the history of how ammeters faded away.

In the days of generators and early alternators, the voltage regulator was a separate device external to either (remember that little black box on the firewall of the 356?). Apparently, these regulators could be adjusted and an ammeter was useful in adjusting them so that they charged a small amount when the engine was at idle, with all electrical devices (lights, wipers, etc.) turned on.

But once the regulators were moved inside alternators (and could no longer be adjusted), an ammeter served little purpose and could be replaced by the cheaper 'ALT' light, and that also eliminated the need to run heavy current (and expensive cabling) up to the dash.

This is, again, from just some YouTube video, but it sounds truthy enough.

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@Sacto Mitch posted:

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I was wondering how that all worked and did some sleuthing of my own.

Found a YouTube video by a mechanic who seemed to know his stuff, and he explained the history of how ammeters faded away.

In the days of generators and early alternators, the voltage regulator was a separate device external to either (remember that little black box on the firewall of the 356?). Apparently, these regulators could be adjusted and an ammeter was useful in adjusting them so that they charged a small amount when the engine was at idle, with all electrical devices (lights, wipers, etc.) turned on.

But once the regulators were moved inside alternators (and could no longer be adjusted), an ammeter served little purpose and could be replaced by the cheaper 'ALT' light, and that also eliminated the need to run heavy current (and expensive cabling) up to the dash.

This is, again, from just some YouTube video, but it sounds truthy enough.

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Thanks for the response Mitch  All seems to be working now with the three wire junction terminal I bought from Lowes.  I think I need to run one more small wire in that junction from the B+ circuit from the Alternator to cover the battery warning light in the VDO gauge.

I need to go back underneath the dash one more time tomorrow to install the GPS sending unit.  Will update on the progress

Do yourself a solid and put some fingers on that junction when the car is running and the power is being drawn. Make sure it ain't too warm.

One note that the large B+ wire from the Alternator needs to be connected to a switched connection in the ignition so the circuit from the battery to the alternator is only active while the car is running.  I noticed the B+ terminal was always hot and verified it should only be hot when the key is on...

Will definitely keep note of the temperature of the junction terminal Ed.

Thanks again to everyone!