512 BBi Blown Ammeter Shunt

Here is the story. I started experiencing the generator warning lights coming on while driving at night with the headlights on. During the day, no headlights, no warning lights. Cleaned the fuse box connections. The fuel pump connections were corroded and cleaned those as well. Car started and while driving I turned on the headlights and boom, the car stops. No power, no juice. Towed the car home and discovered a badly burnt ammeter shunt. I could get the juice back by wiggling the main electrical wire but once I tried to put the car in motion it would stop again. I can and will replace the shunt but would sure like to understand what caused this. Ideas?

Hi Peter, Welcome to FRalk.

Which Shunt?

The one beneath the passenger side footwell?

That's the one. It is identified in the book as the ammeter shunt.

If you're talking about the big green rectanguar piece with thick brass ends this is protect the cars electrical system in case of a battery/battery cable short to ground or against hooking a battery up backwards. If it has a problem my guess is someine installed the battery cables backwards, probably briefly, at some point in the past.

Regards, JRV

So are you thinking that I just replace the part and hopefully the next time I turn on the headlights the same thing does not happen?

Peter,

that shunt is actually a big industrial fuse of sorts. It was likely damaged but not completely blown connecting a battery backwards. The current draw from the accesories (lights, AC) finally killed it. You may also have a charging problem, but one thing at a time. Replace the shunt and repair any wiring and/or connector issues at the shunt and go from there. Alternator problems are not that rare on BBi's but first things first.

Regards, JRV

Thank you. I found the part at Ferrari Clasic Parts. Do you know where I may be able to find the part in the USA? And thanks for the help.

I purchased one from Algar a couple years ago after a gas station replaced a BBi battery.