2155 Ammeter wiring (I'm lazy...)

kgschrader · May 29, 2008

Yes, I have the wiring diagrams, but I'll admit it, I'm a little lazy....

When my car is running, EVERYTHING goes through the ammeter.
i.e., the ammeter is measuring the total current being consumed, not what is being used to charge the battery.

If the lights are on and the A/C is on, the ammeter is off the scale big time. In fact, I rarely see the ammeter needle except at idle when everything is off.

Where would be the best place to start looking for the wiring correction I need to make?

I had a wiring problem when I first got the car where a left turn signal lever actuation would blink the right rear and the left front and the fog lights wouldn't work. It was eventually an easy fix (wires were crossed in the plugs at the front of the car), but it took me hours to find.

Any suggestions?

Thanks,
Kirby

576103 · May 30, 2008

kgschrader said:
When my car is running, EVERYTHING goes through the ammeter.
i.e., the ammeter is measuring the total current being consumed, not what is being used to charge the battery.

If the lights are on and the A/C is on, the ammeter is off the scale big time. In fact, I rarely see the ammeter needle except at idle when everything is off.

Off the scale big time? Meaning that it is showing a full discharge, or a full charge situation?

David Morton · May 30, 2008

fROM THE INTERNET:

Wiring for Ammeter or Voltmeter

A short description of how to wire in an ammeter or voltmeterfor your car.
The ammeter shows direction and rate of current to and from thebattery. Under normal conditions, the meter should show a (small) charge. This will be higher after starting, but probably never more than 10A, and often about 1A. If you see a discharge reading (other than maybe at tickover) you're running on borrowed time.
The voltmeter also indicates whether the battery is being charged. A reading of ~12V indicates that there is no current flowing into or out of the battery. Less than 12V indicates discharge (typically 8V when cranking the starter) and 13-14V is a healthy charging voltage. More than 15V when charging indicates a faulty regulator on the alternator.
A voltmeter actually shows more information than the ammeter, and is also safer to wire insince it takes no current and this allows the use of a small (1A or less) fuse. The ammeter needs to take the full normal load. This is 30A or so for a Seven, but add a few extra lights etc. andit could be more.
Here's an artistic pic. of how both could be wired in.

P2164 · May 30, 2008

A voltmeter actually shows more information than the ammeter, and is also safer to wire insince it takes no current and this allows the use of a small (1A or less) fuse.

Very true and also amp meter connections create problems. I plan on doing away with my amp meter and replace with volt meter. I would bet the meter in my car is not calibrated and just to show a charge or discharge. With the battery disconnect off it still shows a slight discharge. POS and going by by soon. The large spade connectors SPF uses WILL be a problem in the future. Any Ferrari pre 1990 owner who has spent hundreds or thousands of dollars replacing window motors and seeing dim lights should listen up and go to the source of the problem which is those spade connectors. On Ferrari used as a disconnect for the main buss.

P2164 · May 30, 2008

Kirby, you need to visit me for an evening on your way north, I will fix those problems for you in a jiff.

kgschrader · May 30, 2008

Mike Drew said:
Off the scale big time? Meaning that it is showing a full discharge, or a full charge situation?

Sorry, apologies. I should have been more clear. Charging.

I've checked. It is not overcharging, it's just that the ammeter is showing every amp drawn instead of just what is going to the battery charge, as is typically what is shown.

Turn the lights on and the ammeter jumps to the right.
Turn the A/C on and it jumps even more to the right.
To the point where the needle is buried and you can't see it.
No other problems exist, the battery is fine, the alternator is fine, etc. etc

I gave rides last month when I had a 'garage warming' party and Mike Trusty helped tune the EFI some more. It runs fine!
I've got to do some balancing of the TB's, but, as I've told others, it's the fastest thing I've ever driven!

I was hoping someone else had seen this issue on an SPF and could point me straight to the problem. Otherwise, I'll do some sleuthing and find where it is incorrect. And give Dennis O a call also...

As for the voltmeter vs. ammeter argument, Jack, it's my contention that if you want to _really_ know what is going on at any time, you need both.
Just and old fart BSEE opinion....

Thanks for the input, guys.

Things to do this weekend...
- balance TB's
- install fire suppression system
- adjust rear clip so it's straight
- mow grass
- etc. etc. etc.

Kirby

576103 · May 30, 2008

kgschrader said:
I've checked. It is not overcharging, it's just that the ammeter is showing every amp drawn instead of just what is going to the battery charge, as is typically what is shown.

Turn the lights on and the ammeter jumps to the right.
Turn the A/C on and it jumps even more to the right.
To the point where the needle is buried and you can't see it.
No other problems exist, the battery is fine, the alternator is fine, etc. etc

Still confusing, if you don't have a Superformance sitting in front of you. :huh:

Is 'to the right' towards the positive (charge) side or negative (discharge) side?

All the car electrical draws should be on the negative side. With the key on, motor not running, actuating anything electrical should result in a discharge indication (which is normally the needle moving to the left). With the key on and the engine running, the needle should be showing a slight charge at anything above idle rpm. Increasing electrical load (say, by turning on the headlights, or the A/C) should initially result in immediate movement in the direction of discharge (perhaps not into the negative region, but at least movement in that direction), followed instantly by the needle returning to its slight charge position as the voltage regulator steps up the alternator output to compensate for the increased draw.

Your description makes it sound like both the load and the charge wires are hooked to the same side of the ammeter. This would cause the needle to move towards the positive side whenever there is power applied (that is, the alternator is charging) and move even further to the right when a load is placed on the system.

That ain't right!

I can't comment on the construction of the SPF ammeter itself, but it sounds like there are better GT40-correct ammeters available out there. I'm not sold on the idea of a voltmeter being a better substitute, because although it shows total electrical charge available, it doesn't actually show that the charging system is really functioning. Your alternator could quit, and the voltmeter would just slowly drop, which would be difficult to discern. When an alternator quits, an ammeter shows a pronounced discharge when an electrical load is produced, which is quite apparent right away.

I was photographing a Pantera last weekend; the insulator inside the alternator gave out and shattered, and pieces of it jammed the stator, locking up the alternator solid for a few moments at a time before the piece of debris would break. Besides the smell of burning rubber and the sound of a belt slipping, the ammeter told the tale right away, whereas a voltmeter wouldn't have shown anything significant.

kgschrader · May 30, 2008

Mike Drew said:
Still confusing, if you don't have a Superformance sitting in front of you. :huh:

Is 'to the right' towards the positive (charge) side or negative (discharge) side?

Your description makes it sound like both the load and the charge wires are hooked to the same side of the ammeter. This would cause the needle to move towards the positive side whenever there is power applied (that is, the alternator is charging) and move even further to the right when a load is placed on the system.

That ain't right!

Indeed.... Gee... I've NEVER seen an ammeter go to the left when charging, but then... what do I know...

Seriously...
I called Olthoff Racing and they know about the problem. Some cars have it.
And... have a fix.
I'm waiting for Dennis to get back to me.

Should have done that in the first place, but hey... we wouldn't have had all this fun!

Later,
Kirby

P2164 · May 31, 2008

Mike, I will disagree with you on the voltmeter, the voltmeter will give you potential energy as an amp meter only show kinetic energy. You can show a 50 amp charge rate on the amp meter and your alternator can be max'ed out and battery can only have a 10 volt potential. This means you have a dead cell and when you turn your car off it will have a low battery, without a volt meter you don't know. A voltmeter will be tell you if you have a problems far ahead of an amp meter. I have ordered one to replace the amp meter. Next time you look at the 65 Jag XKE, look closely at the amp meter, I think it shows charge to the left.

minerl · May 31, 2008

I posted a "How To" a few months back on how to install a voltmeter in place of the SPF ammeter. I agree that a voltmeter is better than an ammeter for telling you what is actually going on in the charging circuit. However, for the guys that want to stay with the ammeter, below are diagrams on how the wiring should be done to fix the problems with the SPF cars. The problem stems from the fact that the factory wires the ammeter such that it is placed on the wrong side of the load in the system. What complicates it even further is that some cars have this problem while others do not. It seems to be a quality control issue to me. Be that as it may be, here's how to fix it or change to a volt meter.

You will notice that there are two version of the fix, one from Cantor (the harness manufacturer) and one from Dennis Olthoff. I personally like the Cantor version better but either will work.

kgschrader · Jun 2, 2008

minerl said:
I posted a "How To" a few months back on how to install a voltmeter in place of the SPF ammeter. I agree that a voltmeter is better than an ammeter for telling you what is actually going on in the charging circuit. However, for the guys that want to stay with the ammeter, below are diagrams on how the wiring should be done to fix the problems with the SPF cars. The problem stems from the fact that the factory wires the ammeter such that it is placed on the wrong side of the load in the system. What complicates it even further is that some cars have this problem while others do not. It seems to be a quality control issue to me. Be that as it may be, here's how to fix it or change to a volt meter.

You will notice that there are two version of the fix, one from Cantor (the harness manufacturer) and one from Dennis Olthoff. I personally like the Cantor version better but either will work.

Well, somehow I missed that! Thanks very much for documenting that. I did call Dennis and though he was out, I was informed that there were a few cars the same as mine and there was a fix.

So, I have the method, now I just need to implement!

Thanks again,
Kirby

kgschrader · Jul 8, 2008

As an update... I implemented the easy fix on the ammeter wiring.
I cut the wires and swapped them back near the large 80 amp fuse block.

With the key on, the ammeter then read backwards and I had to swap the wires on the ammeter. Everything worked, but then I found out why I always seemed to have a low battery....

With fans on, it would charge, but not much. With the A/C on, next to no charge. With the fans, A/C and lights on... big time discharge.
I could never see this before as the ammeter was reading total system current.

So I put a new 130 amp alternator on and everything is fine.
Still charging with everything on.

I also added a voltmeter.

FWIW,
Kirby

rasigl · Oct 25, 2009

Original post deleted

2155 Ammeter wiring (I'm lazy...)

Kirby Schrader

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Mike Drew

David Morton

Jack Houpe

Jack Houpe

Kirby Schrader

They're mostly silver

Mike Drew

Kirby Schrader

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Kirby Schrader

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