Older Hyundai Santa Fe - Complete electrical failure, but rad fan running

[Number_35]

I passed an older Hyundai Santa Fe earlier this week, with the hood up, and noticed they had really flimsy-looking booster cables but no access for a boost vehicle. I had a booster pack in the van, so stopped to help.

Strange thing - the battery gave every appearance of being completely dead. No headlights, running lights, or brake lights, and yet, weirdly enough, one of the electric fans was running. (Not sure if it was for the rad or for the AC condensor.)

A boost off my booster pack did nothing.

Checked in the fuse box under the hood, expecting to see an open fuse or fusible link, but everything looked OK. (There was a big 175 A fuse that fed everything else - it appeared to be fine.)

I was unable to help, and had to leave them, albeit with roadside assistance on the way.

Realized I need to carry a multimeter or 12 V test light in the van. I felt pretty helpless without any equipment.

It's possible the fan relay failed closed (completing the circuit) and the fan running drained the battery, but if everything else was so completely dead, why was the fan running?

It's unlikely I'll find out, but has anyone here experienced something similar? Any theories?

Thanks.

 

[D60]

I carry a DMM in every glove box.

Beyond that, no help

 

[Number_35]

I carry a DMM in every glove box.

Beyond that, no help

My plan going forward. Lesson learned.

 

[twX]

The battery might have been so drained that it was only putting out 6 or 7 volts while it was under load. Electronics will refuse to operate under a certain voltage, but a DC motor will still work (at a lower speed). Could also be a shorted cell in the battery reducing the voltage.

 

[D60]

My plan going forward. Lesson learned.

Do be sure to regularly replace the 9V. Also I'm unclear on the long-life lithium types, ie if they're advisable for DMMs, but pretty sure I have one or two in some of my glove box units