Failed Gauges and Battery


Tomcat

Tomcat

GT Owner
May 23, 2013
1,337
Perdido Key (Pensacola), Florida
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 an 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)!
 
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Yep. Battery first
 
Yep. That also happens with a good battery that is simply low on charge.
 
Good. Relief
 
Same thing happened to me. Low battery and my gauges worked intermittently. New battery and everything works great.

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

QSS
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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.
 
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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.
 
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.
 
I am appreciating PeteK/HighHP/Kendall discussion...I got Cs in electrical engineering classes (after taking them twice).
 
Random battery question: Would your battery completely die if you left a door(or front/rear compartment) open and it was on a tender, and it was sitting for a month or so?
 
Vinithing said:
Random battery question: Would your battery completely die if you left a door(or front/rear compartment) open and it was on a tender, and it was sitting for a month or so?
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Depends on the maximum output (amps) of the specific tender and the draw of the energized components (lights/computers)...it might overwhelm/overheat the tender electronics causing failure.
 
It’s the Battery Tender Jr. I believe, the one that I was recommended from this forum. Rich hooked up the terminals and ran it through the front end for easy connection. One strange thing I noticed is that one of the rear break lights is out whenever I put the key in the ignition and the battery is dead. Not sure if that means anything…
 
Tomcat said:
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.
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Yup, me too. Always wait a few seconds to let the gauges initialize before I start er up.

QSS
 
Had this on my car about a dozen times over the years. The gauges have always woken up with good voltage
 
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