alternator + electrical niggles

[sierraspider]

Couple of things

!. Charge/oil pressure lights not working when I turn on key
2. How do I check alt output. New battery keeps discharging

[RRoller123]

I haven't done it, but I believe that you can take the Alternator to any Advance Auto Parts, etc. store and they will test it for you for free.

[GeorgeT]

1. Check the bulbs and the grounds for the lights.
2. You can drive your car to Advance Auto or similar store and the can check the battery and alternator without removing the alternator, that's how I found my alternator had a bad diode.

[RRoller123]

Good to know, I thought you had to bring the Alternator in to a test stand in the store.

[Nanonevol]

If you put a simple voltmeter on your battery it should read 12 volts and go up to 14 or so when the car is running. That would show it's charging.

[Nanonevol]

If you put a simple voltmeter on your battery it should read 12 volts and go up to 14 or so when the car is running. That would show it's charging. Or not.

[sierraspider]

Thanks all... Will check out and get back

[MonitorSteve]

I know this is an old thread but I’m struggling with my 1976 Spider. The PO of the car made a few modifications that I have sorted out. However, I’m now struggling with being confident the alternator is charging the battery. When not running the battery shows 12.48 volts, when running I get 12.37-12.38 (wired my trusty Volt meter to the battery on long leads). When the engine hits 190 the voltage drops to 12.22-12.25 when the electric fan comes on. All the boards say I should have 13.5 or so volts when running. I don’t get anything like that. I have a new/rebuilt Martinelli alternator and a new solid state voltage regulator I had the local auto electric shop test the alternator and voltage regulator and they said it tested fine. I’m fairly sure the owner was there when electricity was first put to use.

The grey wire from the alternator to the voltage regulator shows between 11.88 and 12 volts exactly when running and the other side shows no more than 12 ever. The red battery charge light never goes out and the voltage does not drop during a drive unless electrics are put to use like headlights or the radiator fan.

I’m ready to sell this car but don’t want to if there is something wrong. Has anyone seen anything like this before or have any further ideas on what to check?

Steve V
Monitor WA

[spider2081]

The 76 Spiders were delivered with a Magneti Marelli alternator. This alternator uses a remote voltage regulator and a remote relay that operates the "battery warning" light

THere are 2 push on spade terminal connections on the Marelli alternator. The gray wire from the voltage regulator goes on the field terminal. The other wire is Yellow/red and goes on the other terminal. I don't remember how one tells the alternators terminals apart but the wires must be connected to the correct terminals for the alternator to operate properly.
The "battery warning" light is powered from the ignition switch "run" position and the remote relays contacts supply the ground for the light to be lit when the relay is not activated. The relays coil is connected directly to ground, when the alternator is working the alternator outputs voltage on the yellow/red wire that activates the warning light relay. this removes the ground for the "battery warning" light and it goes out.
If a diode shorts internally in the alternator battery voltage is present on the yellow/red wire when ever the battery is connected in the car activating the "battery warning" light relay. If this occurs the "battery warning" light will not be able to lite and the battery will drain through the relays coil in a day or 2.
If when you make the final connection to your battery you hear a slight clicking noise toward the front of the car check the yellow red wire on the "battery warning" relay for voltage is there is any that is a problem.

[Stephen2583]

Hey guys, I’m having a similar issue with my ‘76. I recently replaced the alternator and got the “battery charging system fault light” to go out. However, I’m still not getting 13.5-14v at the battery when the car is running. I gave it a chance to warm up and pressed the accelerator some to see if the charge went up, but no luck. I’ve also replaced the battery charge relay to make sure the system was operating properly. Any suggestions would greatly help.

[spider2081]

Any suggestions would greatly help.

For the charging system to function properly all the electrical terminals must be clean and tight. This includes the battery terminals The battery's ground connection to the chassis, the push terminals on the voltage regulator and alternator. Also the large pink wire connection to the fuse panel. The alternator grounds through its mounting so the mounting areas should be paint free on the engine and alternator.
Have you replaced the voltage regulator?
I think the battery warning light will go off when the alternator is putting out enough voltage to energize a 12 volt relay. So ( i'm guessing} maybe anything over 10-11 volts will turn the light off even though that is not enough to charge the battery.

[gbsailing]

I have found that new alternator and the solid state voltage regulator will still show no charge even though they both test separately good but combined are not compatible. In that situation I always go back to the original style voltage regulator and the system works fine. Solid state on a lot of older vehicles don't always work property as resistance in the old systems sometime affect the electronics in the solid-state adversely. Try using a non solid-state regulator and see if that will correct the charging.

On older wiring systems a lot of people check the positive wiring real close but forget that the ground is just as important and a lot of time it is the ground system at fault. With the ground system using the whole body as with the battery in the trunk it only takes one rusted or poorly fastened panel to adversely affect the whole system so defently check all grounds closely.

[spider2081]

Hey guys, I’m having a similar issue with my ‘76.

Has this issue been resolved??
Have you checked for voltage on the green field wire at the alternator?

With the ignition key "on" and the engine not running the field wire (green) needs to have some voltage on it to "excite" the alternator when it starts spinning. I would expect this voltage to be close to battery voltage.

[Stephen2583]

Yes!!! The issue has been resolved. I wasn’t getting power to the black wire off the ignition to starter. The previous owner had spliced a wire in and done a terrible job. I fixed the wire and she purrs like day one!!! Thank you all for the help!!!

Hey guys, I’m having a similar issue with my ‘76.

Has this issue been resolved??
Have you checked for voltage on the green field wire at the alternator?

With the ignition key "on" and the engine not running the field wire (green) needs to have some voltage on it to "excite" the alternator when it starts spinning. I would expect this voltage to be close to battery voltage.

[spider2081]

great to hear
Enjoy your ride