Failed Gauges and Battery

[Tomcat]

I have to THANK the brain trust here. I kept putting off replacing my battery (as I had no issues and keep the car on a tender). Anyway, last weekend I lost 4 instruments on initial start (Tach, oil pressure, vacuum/boost, and Speedometer)...some big, some small. I immediately got a Optima RED25 and did the switchout. All the gauges came back and no warning lights.
Thank you all (as there are dozens of write-ups)!

 

[twobjshelbys]

Yep. Battery first

 

[HighHP]

Yep. That also happens with a good battery that is simply low on charge.

 

[GTdrummer]

Good. Relief

 

[QuickSilverShelby]

Same thing happened to me. Low battery and my gauges worked intermittently. New battery and everything works great.

QSS

 

[Tomcat]

Same thing happened to me. Low battery and my gauges worked intermittently. New battery and everything works great.

QSS

I hope we didn't do any long-term damage/weakening. I DO religiously allow for the ignition key to initialize the odometer BEFORE hitting the start button.

 

[PeteK]

Hypothesis: The battery low voltage doesn't affect the gauges, per se, but instead the gauge sending unit. That would make more sense to me electronically, especially if multiple gauges are affected. Does anyone have good insight into how the sending unit works and whether that might be the cause of gauges going wonky due to battery voltage? Yes, I know, the gauges also fail separately, but that's not what I'm asking about.

 

[HighHP]

I think the gauge activation is controlled by the gauge module. nota4re has a some good write-ups about why this happens.

My 2014 Mustang GT500 does the same thing. If the battery is low (a good battery) certain systems, like the touch screen and related systems, will not work. They will not start no matter how long the car runs. The ignition needs to be turned off and back on. On restart, with a charged battery, everything starts as expected.

 

[Tomcat]

I am appreciating PeteK/HighHP/Kendall discussion...I got Cs in electrical engineering classes (after taking them twice).