Veg, as described above, the left side heater box component is for the two speed fan. When you are rebuilding the heater box, check this component with your voltmeter to make sure it is isolated from the heater box; I can't recall the details but mine was making contact with the heater box which was putting a voltage on the box.
The component on the right side of the heater is a standard Lucas Make and Break relay. It is used in a latching relay circuit to allow the side lights to operate using the intermittent rocker switch next to the vacuum headlight switch. A Bosch type relay can be substituted for the Lucas relay if you are rewiring the entire car and using modern relays.
The circuit is also latched by one of the light switch microswitches. The microswitches I am referring to are (in my Federal car) small rectangular units located integral to the headlight vacuum switch, not located at the headlight pod. Here is an Allied Electronics call-up for an exact replacement for the vacuum switch microswitches; the model number and brand have changed / superseded over time, but this one fits correctly with the stock mounting plates. The first thread link has pictures of the microswitches installed on the vacuum switch.
lotus-electrical-f38/vacuum-head-light-switch-valve-t30012.htmlhttp://www.alliedelec.com/johnson-elect ... E12D18A442 This circuit can be a bit confusing to discuss as I expect there are variants by Plus 2 model that do not use the intermittent rocker switch and relay setup. Here is a post I prepared with a Powerpoint wiring diagram and the side light circuit description
lotus-electrical-f38/side-lights-t17589.htmlI can't find it right now, but I think someone else here prepared a schematic style drawing of the same circuit if that floats your boat.
Not sure if you got an answer regarding the ground strap with the plastic covering. This strap is attached to a bolt on the rear of the stock radio to suppress static. IIRC the other end of it is grounded with all the other Black ring connectors at the right side dash bracket bolt.
During my rewiring project I actually used a ground strap (might have been that radio one?) to move all of the Black ground wires to a remote nut and bolt as a sort of ground bus. I figured this made it easier to do all of the ground connections and testing with the dash on the bench. As I was using a lot of relays and fuses in my revised wiring, I mounted relay and fuse blocks on the back wall of the glove box; all of the components can be accessed from inside the glove box where that stay nice and dry. With this setup it was very easy to test the entire loom outside of the car, and it minimizes the number of wires coming out of the dash.
Regarding the ammeter wire, I changed the ammeter to a voltmeter. My Plus 2 Workshop Manual actually includes a section for conversion, and says it should be changed if upgrading the car to an alternator. Electrically the ammeter wire carries all of the current other than the starter motor, whereas the voltmeter only requires a light gauge wire to monitor voltage with a very low current. If you go this route, I found it difficult to get a Smiths voltmeter with an exact matching bezel design. I ended up using the needle cover from my ammeter as a substitute for the round needle cover on the voltmeter i bought on eBay UK.
Plus one on rebuilding the heater. The foam seals will be completely gone, which makes the car unbearably hot in the summer. Not sure if explained already, but the Plus 2 (unlike the Elan) does not have a coolant valve in the heater circuit, so the heater core always has hot coolant circulating. Once the foam seals on the bottom flap have failed the heater leaks warm air in to the cabin constantly. I also added an in-line coolant valve to the heater circuit, but I would definitely start with a proper replacement of the foam on the flaps.
As you are probably going to launch in to the heater box job, might want to think about a popular mod to provide more mounting depth for the radio. I did a form of this mod, but was still not able to mount the single DIN head unit I bought. YMMV. Not an issue if you are using the stock or a period substitute radio, but worth consideration while you have the car apart.
HTH
Stu