Alternator charging problem

[mdrburchette]

Hi all.  My 76 131 has a problem with the alternator not charging.  The charge light comes on when the key is turned then it stays on while driving.  The previous owner has aded an amp gauge and as I drive I can see the battery slowly being discharged.  I assume the 76 came with the Magnetti Marelli alternator but the previous owner has replaced it with a Bosch with internal regulator.  I have taken the alternator off and had it gone through and it is good.  I also replaced it with another known good one and it still has this problem.  My question is, does this car have a charge light relay?  If so, where can I find it?  And also, can someone show me where the external voltage regulator was mounted from the factory?  I think I'm dealing with the field wire is maybe not correct due to the change from one type of alternator to the other.  Any help is appreciated!
Denise

[Thotos]

Hello Denise and welcome to our forum.

All alternators need 12V going in before they can give anything out. Unlike dynamos, alternators don't have permanent magnets so need 12V on their yoke to produce the required magnetic field. There should be 2 wires going onto the alternator. Probably you have more than 2 on yours due to the extra instruments but you'll only have 2 connectors. The bigger screw terminal is the output but the smaller spade connector is the input. The wire to this spade connector should have 12V on it when the ignition is turned on. Normally this wire is fed from the charging light so once the output of the alternator is above 12V the charging light goes out.

It's a long time since I've owned a Series 1 131 with external regulator but from memory the external regulator is mounted on the right-side inner wing at the top near the bulkhead (firewall for you Americans  ). I'm sure one of our Series 1 owning members will confirm that.

[mdrburchette]

Thank you for the welcome!
The exciter wire seems to be acting opposite of how it should work.  The Marelli alternator on my 72 Spider had 4 wires coming from it.  One to the battery, one to the voltage regulator, one to the charge light relay and one to the ignition switch.  The wire to the external voltage regulator should be the one eliminated.
    When I turn the key on, the alt light comes on.  When the alternator starts charging, it should excite that circuit and cause the light to go off.  I'm thinking maybe the original owner has the wrong wire going to the light.  Hopefully someone can tell me what color wires go where so I can determine if it's wired correctly.

[Tas131]

G'day Denise,
Glad to see you've come over from the dark side of 124 ownership! Is your 131 a twincam or pushrod motor? I've got a Fiat original factory manual for the series 1, dated '76 or '78 or something. I can check the wiring diagram and let you know what wires go where if you like, or better still, PM me your email address and I can send you a photo.

[mdrburchette]

I haven't completely crossed over, Mick.  I've only added to my collection of Fiats.  Love my Spiders and X19s too!  PM sent.  Thanks for any help you can give.  I have a shop manual for this car and an owner's manual but no wiring schematic in either.

[mdrburchette]

I want to thank Mick for sending me the wiring schematics for my car.  This will help a lot.  I'll be pulling the ammeter and voltmeter out and working on getting the wiring in order and let you know how it comes out.  Thanks all.