Testarossa battery light on with engine running

you may first check the voltage output ( thick wire ) at the alternator, so if there is more than the battery has. if so then you have other problem than with the alternator or regulator.
the "not charging light" gets plus from the ignition key and minus from the alternator when engine not running. when engine runs then the minus from the alternator will change to plus and so the "not charging light" will get plus from both sides and so get off

 

It seems like your alternator has failed. To confirm, measure the voltage across the battery terminals with the engine running. It should be about 13.5V. If it is in 12V range then the alternator is not doing its job.

Remember to take both the rear grill and the rear part of the grill off to get to the alternator. I couldn't get the alternator out without taking both these parts off.

Good Luck.

 

You can check the voltage at the cigarette lighter while the engine is running. A healthy charging system will put out around 13.4+ volts, depending on the car and battery state of charge. Anything less than that would indicate a probable fault. I'd say it would be in the regulator or a blown diode in the alternator... perhaps worn brushes. Any of it should be repairable/rebuildable by an alternator shop.

 

Check the battery terminals and make sure they are clean and tight. Don't start buying parts yet.

R

 

meter 2 I would say is not working right
when the engine is off the battery never has 13 V. even if you charge the battery with a charger and the battery is complete loaded it never has 13 V. may be directly after charging, but 1 hour later never.

you have those 14,6 V at the testarossa at how many rpm?
I would also check how much V you have when you switch on the lights, the AC and wait until the fans will start. please let us know the V then at idle and at about 4000 rpm

the voltage at the new car seem for me not so correct, normaly it has to be 14,4 V at about 1500 rpm and higher

as I see it the alternator is working fine, but you may test the voltage under load also

you used a digital voltmeter or an analog? the digital not shows all if the voltage will vary or change fast. at the analog you just see the pointer moving

when you tested at the alternator with meter 2 where you took ground from?

 

Based on those voltage readings I would say the alternator is working fine. So no need to remove it yet.

It sounds like a bad connection somewhere in the indicator light circuit giving you a voltage imbalance. I don't have TR wiring diagram, but if you have access to one, you should be able to trace the circuit and check all he connections.

I also think you need a third voltmeter to arbitrate between your two existing meters. My guess would be that meter #2 is optimistic and might need a new battery.

 

The voltage regulator circuit has its own generation coils and diodes in the alternator (next to the main coils). The bulb illuminates if there is a voltage difference between the two generation circuits.
It is possible that the generation circuit for the voltage regulation is going bad. It has three coils and diodes, them failing one by one can explain for the worsening symptoms. It also means voltage regulation of the alternator output is compromised.
If reachable, and if it can be done safely, measure the voltage on the small wire to the alternator while running. If it differs much from the primary voltage, there is a problem in the alternator and it has to be exchanged.

 

The battery light can turn on if the alternator output is too low, or too high. If the alternator is providing too much voltage, assuming the regulator works, it comes from either the sense wire (yellow) from the alternator plug making a bad connection, or the 9-pin plug under the water tank (although I'm not sure the 87 TR are wired this way). I spent 2 months tracking my alternator problems, and it came down to the sense wire being faulty at these two points. You can see the thread here: http://www.ferrarichat.com/forum/boxers-tr-m/515678-19-volts-battery-4.html

Check these connections before removing the alternator (not a fun job to do...)

 

One other easy thing to do before removing the alternator is to also measure the AC voltage between the two battery terminals with the engine running. It's not always a definitive test, but can give some insight:

If less than ~0.1V AC (IIRC) = a good sign (and how it should be), but something can still be wacky.

If more than ~0.2V AC = a clear sign that the alternator internals have a problem (so forces the decision to remove the alternator with no chance for regret ).

 

Ok it seems this alternator circuit is possibly different from most. If the sensing circuit is external to the alternator, a high voltage situation is indeed possible if there becomes a problem there. Such normally would not produce a situation with an illuminated charging light (but it can easily fry ECU's or other electronics and even cause a battery to crack/explode).

I stand corrected on mentioning an alternator charging circuit having its own coils. While that is possible, most alternators share the coils and have only separate rectifier diodes for the charging circuit.

 

Engine mounts from the bottom (bolt) and top (nut)--only remove the center bolts and only the fwd and aft on the alternator side. You only need to jack the motor ~ one inch to gain clearance (don't over-jack or you will stress the other mounts). The alternator removal is a tight fit--I found it easier to remove the plastic housing on the back for the air cooling hose--it's thin plastic and brittle so use care--one bolt holds it on, and I couldn't remove with the alternator in place only when partially removed. If you lowered the motor after getting the long pivot bolt out you would have more room (I kept it jacked). When you remove the alternator you should find a thick spacer washer sandwiched between the front of the alternator housing and the mount (through the axes of the long bolt)--don't lose that. Here are some photos for reference.
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Now that is good post! Thank you (nothing wrong with altenator in my car but sure as hell I like to remove it)

 

I would absolutely get a good meter to try to figure out what's going on. Based on the numbers you have presented so far, it's far from being clear that the alternator is overcharging.

Your meter #1 is showing 14.6 volts. If accurate, that's not overcharging, that's normal charging. I have a 360 and this morning I took my voltmeter with me along for the ride. On start-up at idle I had 14.8 volts. After a 20 minute drive, the idle voltage was down to 13.7 volts. That's normal behavior.

I would recheck all the connections. Specifically, the culprit may be the yellow/green wire coming from the alternator. On some diagrams, this goes to the panel indicator warning light. I would check it at the alternator connector and at the multi-pin C11 connector under the water tank, if your car has this. And by "checking it", I don't mean just look at it, I would scrape all the contacts (male and female) clean. The behavior of the light as you described indicates a high resistance connection somewhere in this circuit, which may well be a loose or oxidized connector.

On the other hand if you are determined to pull the alternator instead, I would understand your motives. It would give you an opportunity to spend some quality time with your car and it could turn out to be a very satisfying experience.

 

If cleaning all the relevant connector points does not extinguish the light, this would be the next logical step. The "small wire to the alternator" would probably be the yellow-green wire (1GV).

I found a version of a TR alternator schematic in the "19 volt" thread referenced above that I am reposting below. Based on that schematic, if any of the diodes in the trio were to go bad, the light would come on.

That's assuming the OP's TR is wired this way.
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The connector under the coolant tank includes a junction for the charging warning light. I've seen them get corroded badly enough to create excessive resistance and just break off. Either situation will give you a false warning. If you haven't checked there yet, add it to your list.

 

do you have a small scope? then youmay test again.
for me it sounds as if 1 diode makes trouble and with a scope you will see if it is ok or not

the different voltages between cold and warm engine is a result of hte charging of the battery. when you start the engine the battery gives voltage out and when running the alternator gives this used voltage back. and the longer the engine runs the less the alternator has to work. so that with warm an dcold engine is only a side effect and has nothing to do with the charging. but may be when one diode has failure and getting warm that this is is the reason because of getting warm, but has nothing to do with engine warm up

 

Yes, leave the coachwork brackets in place. You won't have problems getting the alternator out of the mount bracket but it is tight getting the alternator out from under the shelf. What I did was once the alternator was free I rotated it and removed the single bolt holding on the plastic air duct, then removed the duct. This gave enough room to get the alternator out plus eliminated the fear of cracking the duct--it's pretty thin. Others have removed the 7-12 plenum but I didn't want (or need) to. Thinking back now I don't think I down-jacked the engine after removing the pivot bolt, which would give you another 1-2" so maybe no need to remove the duct if you lower the engine. Just be careful and take your time, you'll get it out.

Raising the engine sounds daunting but it's not--just make sure you cushion the jack against the gearbox (I used wood) and only jack as little as needed to pull the pivot bolt out. I did this with the rear of the car on jack stands (no lift). Let us know if you need more advice.