Reddit reviews Tekpower TP4000ZC PC Based RS232 Interfaced Auto Ranging Digital Multimeter, MS8220R Alike, Computer DMM

Here is such on Amazon: https://www.amazon.com/TekPower-TP4000ZC-RS232-Interfaced-Ranging-Multimeter/dp/B000OPDFLM

The data it spits out to RS232 (though an optoisolator) is a bitstream of its display drivers and needs decoding at the host end, but there are programs for that for at least Windows and Linux. Pulling together an Arduino Uno program to do that and pass on decoded text as serial-over-USB to the host is on my to-do list; the needed decoding information is posted at: https://sigrok.org/w/index.php?title=Multimeter_ICs&oldid=11625

while looking for a multimeter which offers RS232, i've found a low-cost option which is designed in a way that works similarly to what you've described.

product page ~$30 shipped

product review page with the details.

Many years back I bought a cheapo Tekpower TP4000ZC when it was still in production and cheaper than you can get it now. It has Youtube reviews such as this overview and this RS232 datalogging software overview. (It needs an RS232-to-USB adapter, which are very cheap.) I didn't use the supplied software for datalogging myself, but my own Python code — I see that there's now a Python library for it on Github.

It still works fine, but these days I'd try to find its USB equivalent. Beware that you do get what you pay for. E.g. a cheap USB multimeter, the like this one which has reviews that describe the wrong multimeter and is a rebadged Tekpower TP8236. You can bet that the cheapest meters have software that's too old to run on Windows 10, and require a bit of ingenuity to set up something that works, as this sort of thing did in the past.

The Raspberry Pi cannot measure analogue voltage directly. You need to use an analogue to digital converter (ADC), such as the MCP3008 or ADS1015. However, these integrated circuits normally measure up to a maximum of 5 V. If you want to measure larger voltages you'd need to use another device.

Normally what you do is use a digital multimeter that has a USB port to transmit the recorded data serially.

https://www.amazon.com/TekPower-TP4000ZC-RS232-Interaced-Ranging-Multimeter/dp/B000OPDFLM

Get a serial port-enabled multimeter. And a usb-serial adapter if you computer doesn't have a serial port.

Cheap amazon link

Digital multimeter... here's a couple decent looking ones that should do most of what you want.

Of course Fluke makes the best, but they certainly charge for it.

I have a Craftsman Professional myself and it's perfectly fine.

So it sounds like the thing to do would be to fix the broken speaker wire. There's a number of ways to do that. I'll list them in decreasing difficulty, and also decreasing quality of fix.

You could:

• Run entirely new wire from the factory wiring harness to the speaker in the door.
  
• Find the break and run new wire from the break to the speaker.
  
• Find the break and just splice in a new bit of wire.
  
  The DMM will come in handy for a lot of things (checking grounds, seeing if your RTO is working, checking fuses, verifying continuity of wires - which you're doing here). If you get a good one now, it'll last you years (I've had mine for more than 10 years and I use it at least a couple times a month for all sorts of automotive and household things!).

Something like this should work.

https://www.amazon.com/TekPower-TP4000ZC-RS232-Interfaced-Ranging-Multimeter/dp/B000OPDFLM/

You may be able to get cheaper, but not terribly much. Of course, you'll need to buy or hack some serial connection. Still pretty easy, and WAY cheaper than a multimeter with a USB connection.