Electrical Question

What is the voltage across the battery at say idle and 3000 RPM? It shouldn't be exceeding ~14.5VDC -- if it keeps increasing with RPM you'll need more alt work.

 

Perhaps check your ground strap between engine and chassis - will likely be low down going from the block to chassis rail near the LH rear lower wishbone. These get corroded and then all kinds of funky things like you are describing start to happen....good luck tracking this one down!

 

Good advice above, and maybe I can provide a little background to help you understand more about what may be going on.

First off testing the system voltage while the car is running is a good way to see what's happening with your electrical system. The variation in light brightness and gauge readings you are seeing is a symptom of varying voltage. The two possibiliteis are:

1: at idle the voltage is normal, 13-14V, and rises too high when the engine is turning faster. If this is the case, your voltage regulator is not doing its job of maintaining the voltage at normal. I have had this experience, and it's a bad thing because too much voltage will start frying stuff in short order. And yes, "frying stuff" IS in fact the correct technical term

2: More likely, at least in my experience, is that the voltage is low at idle and rises to normal when the engine (and thus the alternator) is turning faster. As pointed out above, poor contact of ground wires is a very common cause of this problem. But a bad contact in other wires on the charging system could also be the culprit. Any bad connection adds resistance to the circuit and causes a voltage drop, by that classic hit formula known as Ohm's Law: V=IR

As I am fond of saying, if I had a dollar for every alternator, starter, and battery that have been replaced due to bad connections, I'd be driving a Ferrari! So if you find 2 to be the case, the FIRST thing to try is removing, cleaning, and tightening every connection in the charging system, which includes the battery terminals, the connections on the alternator, and all the grounds you can find.

Good luck with it: electrical problems can be a real pain. (Says the retired Senior Electrical Power Generation Equipment Repairer! MOS 52D20 for those who speak Army)

 

Yup. Your VR is being grounded, and you are frying your battery. Been there, done that. My VR uses 2 insulated screws and after 30 years the insulation became brittle and was grounding it. Yours may be the same design? If you it's an easy DIY although there are a few tricky bits, like using a paper clip to mount the brushes back.

Ken

 

Yow! that's a BAD voltage regulator. DO NOT run the car until you get it replaced, you will burn up a lot of expensive stuff.

 

That pretty much confirms what I said: your VR is shorting to ground. The alternator is sending full voltage to the battery and electrical system. Keep it up and you'll fry your battery and any sensitive electronics.

Tightening connections won't fix it. You have to take out the alternator, take out the VR, look at the two screws that are insulated and change them. I've never been inside a Ferrari alternator but it's likely similar to mine in this regard.

Ken

 

Your voltage regulator is stuffed man. Im not sure on your model of alternator, im assuming its a bosch?? The VR maybe an internal or external one. If its an external one,you may be able to leave the alternator in the car and just take the VR out and replace it yourself. If its internal,best remove the alt and take it to the auto electrician that rebuilt it for you. The question is why didnt the guys that rebuilt it,replace the regulator?? They should have done a bench test,which would have told them that the diode pack was working fine, and maybe the VR was fine then(brushes ok,voltage fine ect....)but usually the VR should be replaced everytime an alternator gets rebuilt?? Where i come from anyways. Good luck friend

*note-maybe you should take the alternator elsewhere this time*

 

I just hope you didn't have to spend $3-400 for this the second time around. The rebuilder made a simple mistake by using a non insulated screw I bet; two are and one isn't if it's like my Delco (it may not be). He should fix it for free. He obviously didn't bench test it; the VR is likely good if it was new. It doesn't get ruined by what happened so he better not charge you for a new one!

Ken