Beck TD, Part 31 - Indicators

In 1952, the MG TD left the factory with exactly two indicator lamps on the dashboard, one green (for gas level) and one red (a charging indicator for the electrical system). Back in Part 22, I detailed how I made a green indicator for the fuel level using some fancy LED indicators from Oznium. They look like this:

Today I had something that has been rare lately - an entire day to spend in the shop. I decided to finish the long-delayed indicator project. First, I replaced the other indicator that came in 1952. Like all charge indicators, it is red when it is NOT charging.

In the center of the dash panel, in 1952 MG had a pair of terminals for power - sort of a precursor to the power plugs we use now for chargers and other devices. Those terminals were long gone in Beck TD. One hole was filled with a flat-headed bolt, and the other had a switch mounted for the now-abandoned heater. The clearance was so tight, the switch had to be mounted sideways. Time to go.

I made a simple holder with the right spacing, and a matching piece for the backside. I installed a blue indicator for high beams, and a red one for the turn signals.

The only problem: how to make either turn signal flash a single indicator. If I just tied them together, then both turn signals would flash when I selected either side. The answer is a sort of one-way electrical valve called a diode. If I hooked up a diode to each turn signal, one side could illuminate the indicator, but the diode on the other side would keep that turn signal from lighting. Here's a simple diagram, probably the first circuit I've drawn in a decade or more. The arrow and line on the diode symbol indicate which direction current will flow, and the third diode with arrows above is the LED indicator:

Translating that to physical reality, I decided to attach the two diodes to the left and right terminals of the turn signal switch, and add a connector on the end to plug the positive side of the LED indicator to. The line on the black diodes matches the line on the circuit diagram. After this photo was taken, I covered each "arm" of the harness with shrink-wrap tubing to insulate them.

I hooked the negative side of both indicators to a "convenient" ground. MG enthusiasts know that "convenient" doesn't really exist under the dash of a T-series MG, because the body framework is wood. What would be an easy ground point under a screw is not a ground here, because it is isolated by the wood. I wound up using a bolt I had already installed in the body for something else. Then I clicked furiously with my phone until I managed to catch the light turned on.

I attached the other indicator to the high beam wiring, and I have four working indicators. Twice as many as MG thought was necessary!

Continue on to Part 32...