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Body frame intermittently at 12 volts

When I put the key in the ignition and turn to “run”, dash lights come on and the radio plays. However, when I try to engage something that draws more current, like start the car (and sometimes just turning on the turn signals or headlights - but not always), everything goes dead. I discovered that the frame is now at 12 volts (checked against the battery negative post - see below). However, the system “resets” itself and, with the key in the run position that dash lights are on again. The “reset” time varies from a few seconds to about a minute (or longer). Sometimes, just putting the key in the run position triggers everything to shut down. However, the door open chime is never enough current draw to trigger this (if in fact it is current draw).

I initially thought that I had a bad ground because I found that when I jumped the battery negative post to the frame (strut bolt specifically) the car would start. I discovered the frame was at 12 volts as I was shocked when I tried to remove the jumper cable. Given the above, I have no idea why the car started. I initially thought that the starter coil was shorting out to the frame, but then I discovered that other current draws would initiate the electrical system shutdown.

The car body / frame should be “ground”, connected to the negative battery post. In many cars, they run the negative battery to the engine block, then, from another spot, a second cable between the block and the frame…I would carefully check your negative battery cable from end to end(s). Both the engine block and the car body (frame) should be connected directly to the battery. Remove the cable from the battery post and examine it carefully for corrosion damage and replace any suspect cables…

Without going a ton into it - the ‘body frame is at 12v’ - indicates that you need a new negative bat cable.

You don’t need a new positive bat cable - because circumventing the negative cable - allows the vehicle to start.

To FIX it - just replace the neg bat cable; and maybe a new frame to ground cable. This will fix it. And you cannot always tell by ‘looking’ at a cable if it is good or bad. Sometimes they look good and are bad. A VOM will probably not help in your case; because they use such small voltages and current - so an ohm test - with a large defective bat cable - which is not completely broken - will still read fine.

REPLACE the neg bat cable. Also - the frame reading 12 v is because the neg bat cable is defective. Voltage is a measurement of potential. When you do not have a good connection between the frame and the battery - then yes - you can easily read 12v between the two points - because you have a potential difference. If the cable was correctly functioning - you would not have any difference in potential - and you would not be reading any voltage between the two points.

Thanks very much. I did use a VOM to “verify” that the resistance was “0”, but given your analysis, that is not a good test. This is (one of the things) that was so confusing to me. Much appreciated. Working on replacing that cable now.