What Is This Ammeter Doing?

[JG71B]

Sorry guys. Busy weekend....with the car off it's at 12.9-13V. At idle, nothing on, 13.9- 14V. Running with headlights on, it drops to 12.5 and seems to want to trickle down. As soon as I touch the throttle, voltmeter shows it climb. The 12.5 seems odd. Should it not hold 13 running ? An issue with front light harness/ground possibly?

 

[Dragon Slayer]

Seems normal to me. Head lights large load. As you load a source it has voltage droop, even in regulated systems. Battery seems right for no load. I assume it cranks easily. If so, sounds like battery is fine.

 

[Don Frelier]

So the battery reads 13.9-14.0 Vdc with it idling and the ammeter shows discharge as you showed in your first picture?
Does the ammeter return to center position with everything off?

 

[Dragon Slayer]

So the battery reads 13.9-14.0 Vdc with it idling and the ammeter shows discharge as you showed in your first picture?
Does the ammeter return to center position with everything off?

Good point, amp meter can't read discharge if system voltage is 14V, that would be the alternator voltage and it would be charging to the battery with about a 1.5V difference from your values.

Like I said earlier, I would expect the ammeter to show charge right after start, and tapper off to near neutral depending on battery condition.

So did you ammeter act different before the battery swap, or are you just noticing this now? Based on your voltage and ammeter readings I would guess your ammeter leads are swapped. You measuring voltage at the battery?

 

[JG71B]

For those asking, oil pressure is 80 lb cold and 45 when hot, I need to change out the sending unit but it's hard to get to because it's near the firewall and it's tough to get anything on it to take it off anyway....
Right after starting it goes over to the charge side and slowly comes back towards the middle but once everything settles down it goes to what I have pictured

 

[Bee1971]

Sending unit is easy with a crows foot or a stubby wrench

Any idea what Amp Alternator you are running

Make sure your bulkhead connections are clean and everything looks good

 

[SlinktRR]

Like dragon said battery appears ok. Might check for voltage drop at various points relative to battery negative, 12.5v on charge seems low. As long as you have a mechanical gauge I wouldn't worry about the stock oil sender at this point. Good luck with troubleshooting.

 

[Dragon Slayer]

Are the voltage reading taken initially, or after things settle down and ammeter reading on the discharge side?

As wired from the factory, everything gets to or from the battery thru the ammeter. Only the starter motor has a direct connection to the battery not thru the ammeter.

So to have a higher than normal battery voltage while running (which has to come from alternator) but battery discharging at ammeter can't be correct unless wiring not oem. You could measure voltage at ammeter. Alternator side to ground, and battery side to ground. Based on your initial readings I would expect the voltage to be higher on the alternator side.

The service manual has a good troubleshooting procedure for measuring voltage.

Something does not compute