No Power/Electrical - Battery Fully Charged

[AlexD]

My “WTF” issue of the day.... to be fair, the car has been awesome for the first month I’ve owned it so not many legitimate “WTFs” so far. This one has me stumped though.

1980 Spider (fuel injection) bought about a month ago. Have been working for the past few weeks on getting the exterior lighting working as only a few were functioning. Eventually got to cleaning every ground and connection I could find and magically all the lights are working. Tacking the dash lights next.

Car has always started and run strong. Battery was brand new when I bought it. Yesterday the whether in Suburban Philly was 70* and I wanted to take her out. Starred her up, warmed up a bit, put in reverse and started rolling out when she stalled. Could have been user error with the clutch, but she wouldn’t start back up. Cranked for a second then dead. No electric at all - no crank, no lights, etc. so I assumed battery somehow drained (maybe I overcleaned all those grounds...). Hooked battery up to the charger and was surprised when it said “fully charged” in just a few minutes. Put key in... nothing again.

The only thing working was the clock - heard the tick..tick..tick - until I turned the key that is. Once I turned the key the clock stopped.

Battery is showing 12.6v on the multimeter.

Any thoughts on where to begin troubleshooting?

[AlexD]

Might start with the green wire from the battery to the starter or the brown wire from the battery to the Ignition

[davidbruce]

I would start with the plug going to the back of the ignition switch. Try wiggling it while you turn the key. They often loose contact or the plug or wires melt from too much current. If that doesn't help test the ignition switch. They fail for the same reason. The original switches are often repairable. If you do not have any relays added for your headlights/wipers/starter already installed, adding them will take a huge load off both your ignition switch and the associated wiring. If you don't have a wiring diagram you can download one from mirafiori.com. You will have to register to gain access to the library but there is a wealth of valuable info there.

[18Fiatsandcounting]

Any thoughts on where to begin troubleshooting?

The symptoms sound to me like bad battery connections, or a bad ground from the car body to the engine. I don't exactly recall where this ground cable is located on an '80 spider, but on earlier years, it is a ground strap from the body underside to one of the larger bolts on the clutch bellhousing cover.

Try this: Put your voltmeter directly on the battery posts (NOT the battery cable connectors). Have an assistant (friend, wife, neighbor, amiable fellow walking by on the street, whoever). When you try to start the car, the battery voltage should drop to 10 volts or so. If it drops way below that, your battery is the problem. If the voltage doesn't change much, it's the cable connections.

-Bryan

[AlexD]

I would start with the plug going to the back of the ignition switch. Try wiggling it while you turn the key. They often loose contact or the plug or wires melt from too much current. If that doesn't help test the ignition switch. They fail for the same reason. The original switches are often repairable. If you do not have any relays added for your headlights/wipers/starter already installed, adding them will take a huge load off both your ignition switch and the associated wiring. If you don't have a wiring diagram you can download one from mirafiori.com. You will have to register to gain access to the library but there is a wealth of valuable info there.

Thanks - will start there for sure and hope it’s as simple as that. Fingers crossed. I’ve already got headlight and wiper relays on order and had that project on the calendar for next weekend. I didn’t realize there was a relay for the starter as well but will look into that. I did sign up with mirafiori.com on good advice when I bought the car and have found the library to be very helpful.

[AlexD]

Any thoughts on where to begin troubleshooting?

The symptoms sound to me like bad battery connections, or a bad ground from the car body to the engine. I don't exactly recall where this ground cable is located on an '80 spider, but on earlier years, it is a ground strap from the body underside to one of the larger bolts on the clutch bellhousing cover.

Try this: Put your voltmeter directly on the battery posts (NOT the battery cable connectors). Have an assistant (friend, wife, neighbor, amiable fellow walking by on the street, whoever). When you try to start the car, the battery voltage should drop to 10 volts or so. If it drops way below that, your battery is the problem. If the voltage doesn't change much, it's the cable connections.

-Bryan

Thanks, Bryan!

[spider2081]

The symptoms sound to me like bad battery connections,

Always a good place to inspect and check. Remember that in order to fully check electrical connections, the connection has to be tested under load (current must be flowing). Usually enough load can be reached by having the ignition switch in the "run" position, along with the headlights and heater fan on.

A perfect electrical connection has zero ohms. This is impossible to accomplish in the real world. Low values of resistance in a connection can raise havoc. Sometimes the low value can be less than what a basic ohm meter is capable of measuring. In theses cases voltage measurements across the connection work well. In this case First as mentioned measure the voltage of the battery with the meter leads on the batteries posts. (under load) Should be 11.5 vdc or above. As stated with the ignition switch in the "start" position the voltage should be above 10 volts for a good battery.
To check the connection of the battery's positive connection keep one meter lead on the positive battery post and the other on the positive battery cable clamp. (under load) Ideally the voltage would be zero. Practically the voltage measurement should be between 0-0.5 vdc depending on the amount of current draw. Anything greater than 0.5 volts indicates a poor or bad connection.
The process of measuring voltage across a connection under load is a simple means of testing connections.
To test the ignition switch connectors brown wire connection (under load) put one meter lead into the back of the cars connector contacting the pin for the brown wire. Place the other meter lead into the ignition switch side of the connector in similar fashion.

Other common causes for your issue are: parasitic draw on the battery when the car sits unused. Parasitic draw is a constant small current draw similar to the courtesy light being left on.
Replacement battery cable terminals. Battery disconnect switches. The battery cable connections at the starter solenoid, the alternator output terminal connections.
Another simple battery connection test hold the ignition switch in the "start" position for a few seconds 15-30 if the engine is not cranking. A bad connection will become warm to the touch.

[18Fiatsandcounting]

The process of measuring voltage across a connection under load is a simple means of testing connections.

An excellent point that I heartily endorse. Ohm's Law is handy here: Voltage = Current times Resistance.

Taking the example of a poor battery cable connection and the starter motor, if the connection has a resistance of 0.5 ohms and the nominal current draw of the starter motor is 200 amps, that would imply a voltage drop of 100 volts across that bad connection. However, this can't happen because the battery can only supply 12 volts or thereabouts, so the outcome is that the current is much less, which is why the starter doesn't turn over. In effect, the power of the battery is lost in the poor connection rather than getting to the starter where you want it.

-Bryan