I have the electronic Smith's gauges in my car and they work well. There are a couple of things you may not be aware of.
1. The
oil temp, water temp, and fuel capacity gauges should be supplied with a constant 10V source. Read the following from Caerbont at the bottom of the page under General Gauges Specification:
https://www.smiths-instruments.co.uk/cobra
I used a DC to DC converter from Powerstream to provide the constant 10 volts, as shown in this link:
https://www.powerstream.com/Product3.htm
2. The sending units themselves for the water temp and
oil temp rely on being grounded through the threads, so use a thread sealer that is electrically conductive. I found that Permatex high temperature thread sealant works well. It is available at any auto parts store.
Good luck!