365 GT ammeter fluctuation

My 1969 QM’s ammeter fluctuates wildly when the head lights are on. This causes a dimming in all the lights which is really annoying at night! This is a twin alternator car. When I isolate the alternators by disconnecting the field wires one at a time the problem is eliminated. Hook them both up, problem returns. This 365 being new to me we are sorting multiple issues but this one is interesting! One thing, there is what appears to be a noise suppressor in the main line from one of the alternators to the Buss lug but not the other. The wiring diagram shows both alternators with this item in the main line. Anybody know what this item is? Has anyone had this problem? Picture attached of the mystery item.

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I never heard the term 2 alternator Ferrari. Table 17 of the 365 2+2 parts manual shows a single Marelli alternator, part number 50.35.014-1. Not shown on the figure is a Marelli transistor voltage regulator, part number RTT-101-C. Does you car have these original parts? If so, the next step would be to check all the electical connectors. A common problem with the transitor voltage regulators is the chassis ground. On my 330 I ran a wire directly from the battery negative cable to the bolt on the regulator where the ground wire is attached. On my 330 (Lucas parts) the amp meter does fluctuate when the battery is fully charged and there is no load on the electrical system. The voltage regulator is turning the field winding on and off at a rapid rate. Adding a load to the electical system like turning on the lights reduces the fluctuations. One other comment, the specifications for my 330 alternator are all at 3000 RPMs.

 

The last comment regarding the grounds is very correct. When the regulators have a poor ground their ability to properly control the voltage is compromised. Grounding and other poor electrical connections are a concern on older vehicles. Other areas to look at are the ground straps from the engine block to the chassis, and the battery ground braid to the block. There is a square 4 screw terminal junction block on the electrical panel where all of the heavy current cables join together. This junction block can corrode and cause electrical problems especially at high currents. There are many different metals used in this junction and they easily corrode. Remove the wires and clean all components of this block. As for the capacitors on the alternator, they are to prevent noise in the radio, and have no effect on the charging. Jim

 

Mine does have twin alternators (400i late gen-1 December 1981)

When you disconnect the alternator you basically only rely on the battery, hence the current is homogeneously" flowing out of the battery. As a reminder, what the ammeter tells us is whether current is flowing in or out of the battery (not what the whole current load is on the system).

Aside from the previous comments regarding faulty electrical connections, I would also check the following:

1) When were the alternator brushes & voltage regulator last replaced? (A bad voltage regulator can induce a few current spike in the system, and the higher the current load the higher the voltage spikes). if you have no idea, just replace them, as they are usually cheap and will make your life easier.
2) How old is the battery? (A brand new battery with low internal resistance is more likely to absorb voltage spikes)
3) As far as the condenser is concerned, you may benefit from a new one: the alternator does not directly feed the battery, instead the current has to pass through the ammeter shunt (a heavy duty resistor), this shunt prevents somehow the battery from fully damping the voltage spikes. By contrast the capacitor is directly tied to the alternator output so it can capture whatever spike the battery cannot handle. A big condenser as supplied by MSD can cure most noisy system.
4) Finally faulty alternator diodes could makes lots of ripples in the system: you can check this with a voltmeter set to AC (not DC) and check that there is no AC reaching the battery posts (diodes are supposed to convert AC to DC, if one is missing you get partial AC instead of clean DC).

 

Thanks for all the great replies! The battery is new. This is a two alternator car most US versions with air-conditioning came from the factory that way. The wiring diagram indicates there is no amp meter shunt rather a direct reading ammeter. The alternators and regulators appear to be original. I have no idea about when the brushes were last replaced as I’ve only had the car a few months. I have been going through the wiring system carefully and will look for more additional grounding points. Engine to frame battery to frame all new cables and good clean connections. These high fluctuations only happened under load i.e. all the headlights on at night. Checking the diode‘s in the alternators is a great idea I had not thought of. Will do that soon. I’ll let you know the findings over the next day or so!

 

The interesting fact that this only happens when both alternators are online. If I disconnect one or the other the problem goes away. That’s why I was just curious if the resistor on one alternator and not the other could be causing some sort of an imbalance or feedback.

 

You do have a shunt even if it's built in the ammeter.

The device on the alternator might be used to "load" the alternators in order to avoid each voltage regulators to fight against each others. Not sure it is needed anymore with modern batteries. Maybe that capacitors could do the trick? These used to be installed on old school alternators (not sure about your car though).

Be carrefull not to damage the belts while you make your diagnostics.

 

As far as the ammeter is concerned, on my 400i, I've been analysing the subject quite extensively. The shunt is rougly grabing 0.1v per 50amps. If you do have an built-in shunt, the voltage loss is probably much higher. The twin alternator setup can make it even worse (higher amps = higher voltage loss).

Maybe you should consider to upgrade with separate components (salvage them from a 400) or use voltage regulators that are set slightly higher(?). At the end of the day one way or an other, the battery must receive its proper "topping" voltage.

Also silver conductive grease (the real product made in the U.S. ) can do wonder on stubborn conections...


https://www.ferrarichat.com/forum/threads/ammeter-wiring-1974-365-gt4-2-2.622315/#post-147230013

 

2 alternators is oem. Suspect the original giant radiator fans pulled a lot of current.

 

Plan to keep her oem! This fluctuation happens even when the radiator cooling fans are not operating but when all the headlights are on at anything above idle. There are not many connections in the alternator circuit I have taken each one apart cleaned and reassembled with dielectric grease. Next step is to check the diode‘s to be sure no AC voltage is getting through. I have hopes that is where the problem is! I may try to post a short video so that everybody can see what I’m talking about.

 

My comment above was for the earlier 365 2+2; I agree that the newer 365, 400 series had 2 alternators.

 

Bear in mind that your alternators are working in a kind of ON/OFF mode which may stress the belts (depending on your setup these can be a royal pain to replace).

 

The 365GT 2+2 had 2 alternators. Owned one many years ago and it had 2 alternators and was not modified. The early cars had power vent windows the later ones did not. Mine did not and clearly had 2 alternators and 2 GIANT cooling fans all OEM.

 

Made new battery and engine to frame ground cables today. Tested for AC voltage at the battery, less than 1 volt regardless of which or both alternators were online. Here are a couple of pics and short vid of the ammeter at 65 mph.

 

Did you leave out a decimal point? The AC voltage should be less than 0.1 V AC for a properly working alternator (and usually is less than 0.05 V AC).

 

All the more since the alternators are somehow smoothing each other (the 2 x 3 sinusoidal curves are superimposed)

 

I experienced a similar issue - the ammeter varied widely for no reason. It had never done that before. We changed the voltage regulators to OEM/Bosch units and the problem was solved. They are cheap and relatively easy to get to, so it might be worth a try.

 

Do you happen to know the bosch part number? I will certainly give that a try!

 

This is for my Series I 400iGT - Bosch #1-197-311-028

 

Not sure the "Queen" 365 is using the same alternators as the 400i, probably some Lucas or Magneti Marelli. The regulator might also be external (brush and regulator are separated so one could use a generic voltage regulator, but the brushes still have to be replaced).

The OP could have a look here (https://store.alternatorparts.com/voltage-regulators.aspx) in order to identify its regulator. This being said any alternator shop will immediately spot the proper regulator.

 

Thanks! Yes the 400 and that part # appears to be for an internal regulator. My 365 does have the two external regulators mounted under the driver side dash! They do not have any numbers on them that I can find!

 

Good for you, most generic voltage regulator will do ! ( ex : https://store.alternatorparts.com/il211-voltage-regulator-for-lucas-alternator.aspx , https://store.alternatorparts.com/0192062007-regulator-bosch-alternators.aspx )

However you still have to replace the brushes, depending on how the brush holder is designed, you either have to replace the whole of it, or you can replace just the carbon brushes (these do sell various sizes : http://www.carbonbrush.com/).

Replace the brushes first if this does not cure your problem replace the regulators.