Weird Electrical Happenings-Part 1, ...turning headlight knob effects full gauge Options

[7TPorsh]

I have a bunch of little weird electrical things going on...so i'll attack one at a time:

The fuel gauge (stock combo gauge) moves as follows under different conditions:

- Ignition off/headlights on- turning headlight knob up makes fuel gauge go from empty to full; turning down go back to empty.

- Ignition on/headlights on- fuel gauge show reading...turning knob up increases the reading on the fuel gauge by 1/4 tank; turning down decreases...so 1/4 fluctuation in the fuel gauge depending on how the headlight knob is turned.

Tend to think the full bright on the headlights translates to a closer fuel reading. But why? is the power source for the fuel gauge incorrect?

I checked the schematic, but it looks like a Lucas engineer designed the wiring for the combo gauge.

[7TPorsh]

Where are the ground connections points? Diagram shows a few, and knowing actual locations would be helpful.

Also, what are those little numbers on the wire ends and connections? They don't seem to sync up with each other and it's misleading...should i be grounding every loose brown wire?

[Mike Bellis]

Where are the ground connections points? Diagram shows a few, and knowing actual locations would be helpful.

Also, what are those little numbers on the wire ends and connections? They don't seem to sync up with each other and it's misleading...should i be grounding every loose brown wire?

In the front trunk, behind each headlight
under the drivers side dash, above fuse panel
in engine bay, behind drivers seat

Clean and inspect all 4 of these locations. Also inspect/replace the ground strap from the rear of the transmission to the chassis. Inspect the negative battery cable and connection points.