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Voltage Drops Below 12V at Key On

JedIEG

JedIEG

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I just bought an LM 2 wideband meter and am having issues with the power supply from the car. My interior voltage is dropping to 11.5v when the key is in the run position. The meter requires 12+v @ 3amps through the cigar lighter. At accessory and off the voltage is fine at 12.8v. I put the battery on the charger and made sure it was full and it's a new battery so I don't suspect that at all. Any ideas on what is robbing my power? Coil? ECM? Ballast resistor?
Wiring is a painless performance mopar harness.

I am considering running a wire from the battery to the lighter directly as a stop gap (need to find an inline fuse for that setup).
 
Are you actually running the engine or just have the key in the RUN position? If engine is running and you only have 11.5 vdc on the that line you either have a low charging issue or the ignition switch is dropping voltage in the RUN mode.
 
Last edited:
hook a volt meter between negative and ground. Pull fuses one at a time and see if voltage goes up. If you find one then test for amp draw and pull that fuse again.
 
The engine is not on, just the switch is in the run position.
Unplugged coil + with no change, unplugged the ballast resistor with no change.
 
don't overlook the ignition switch itself. mine was putting out 9 volts in the run position. put in a new switch , now I have 12.
 
snakeoil24 said:
hook a volt meter between negative and ground. Pull fuses one at a time and see if voltage goes up. If you find one then test for amp draw and pull that fuse again.
Click to expand...
This is some very, very good advice
 
⬆️
That's what I tried and sure enough, the wiper motor circuit was pulling power at acc and run. Coil/ignition was pulling a little power along with the guage cluster voltage regulator, but that I expected. With the wiper fuse pulled, voltage is going form 12.8 off to 12.4 run.

Thanks everyone for the help.
 
It's a painless harness so the bulkhead is gone. The wiper harness is continuous from the switch to the motor.
 
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