I finished a little project I started when I had the '91 U300 to monitor alternator output and other future things like battery voltage and engine temps. This project uses these clamp-on current transducers (https://www.amazon.com/gp/product/B00LMPPHGE/ref=oh_aui_search_detailpage?ie=UTF8&psc=1) which output using a 4-20 ma current loop with no shunt required. The 4-20 ma current loop eliminates any inaccuracies due to lead wire resistance. For connection wiring from the engine bay to the cab I used standard RJ11 telephone wire and jacks.
Here are some pics of the display box and where I mounted the 2 transducers to measure the chassis alternator current and house alternator current in the Roadtrek. The display shows 48 amps on the chassis alternator and 161 amps on the house alternator. This was with the microwave running on the inverter at engine idle. The Roadtrek has no generator and uses the house alternator at engine idle to keep house batteries charged and provide 120V power from the inverter when boondocking.
Link to the displays? Do display provide the current for the 4-20ma loop?
Right, there are a few more bits needed to get this current measurement to work. 4-20 ma industrial control loops are typically powered with 24V DC, so I used this DC to DC converter (https://www.amazon.com/gp/product/B00C9179WK/ref=oh_aui_search_detailpage?ie=UTF8&psc=1) mounted inside the display box to supply 24V. Also needed are 4-20 ma current to voltage converters to drive the 4 digit displays (https://www.amazon.com/gp/product/B00BZIBK82/ref=oh_aui_search_detailpage?ie=UTF8&psc=1). I used converters similar to these (https://www.amazon.com/SainSmart-Current-Isolation-Transmitter-Converter/dp/B01H3K1WIS/ref=sr_1_4?s=industrial&ie=UTF8&qid=1495064199&sr=1-4&keywords=4-20+ma+to+voltage+converter) (6 mounted inside the display box). The 4-20 ma current to voltage converters have a zero and range adjustment, I calibrated both current clamps using a hand held clamp-on current meter and my battery load tester and tested at 100, 200, 300, 400 amps for accuracy. To answer your specific question, the clamp-on current transducer is powered with 24V, and provides the 4-20 ma current signal back to the display box where it is converted to a voltage and shown on the 4 digit displays. You ignore the decimal, I adjusted 5.00 volts to equal 500 amps, so for example 1.65 volts equals 165 amps. It didn't cost much, and I needed a winter project to get me through to summer ^.^d