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MG TD TF 1500 - Beginning Wiring

Is there a logical way to identify the positive and negative terminals on the various instruments/lights on the td. Wiring is a major gap in my automotive knowledge.
Bill Reid TD4618

Follow the schematics in the WSM. It identifies what color code wire attaches to which lettered terminal
W A Chasser

I’m with you on that, Bill. RI wiring even supplies a diagram for each section of harness. My question relates to the instrument/light connectors. How do I look at the license plate Light or taillight and know which connector takes the positive and negative wire?
Bill Reid TD4618

Using an AVO or ohmmeter Bill one terminal will be electrically isolated from the body of the holder and hence the tub. The other is the earth. Cheers
Peter TD 5801
P Hehir

Rather than talk about Positive negative, think Hot wire and Ground.
The return current of all the wiring is carried by the ground wire and the chassis.

There is an aftermarket harness, just for the dash. It's about $40. I strongly recommend it.
As I remember the lamp sockets are all returned to ground. BUT the dash requires a separate ground wire that runs from the Speedo to the Tach to the ground on the cluster panel.

I used the MG-T type tubular connecter joiners to connect the prewired dash pigtails to the main harness.

The front fender running lamps depend on making a good ground to the chassis through the mounting bolts, and/or the fender-headlamp brackets. This requires either scraping the paint off around the contact points, or adding SS shakeproof lock washers to penetrate the paint. I added additional Ground wires onto the bolts holding the lamps.

The incadecent bulbs are not polarity sensitive. BUT if your are switching to LED's they may very well be polarized.

I have seen several different License Plate lamp configurations. A Picture would help.


Jim B.






JA Benjamin

Note that the dash wire harness is made for rheostat equipped cars with dished gauges. It does not conform to early gauges without modifications. If doing an early car simply make your own.

Bill Chasser
TD-4834
W A Chasser

Rear Plate Light


Bill Reid TD4618

The ground wire black connects to the left The hot red wire goes to the center below the cover mounting bracket

Bill Chasser
TD-4834
W A Chasser

Got it ....thanks
Bill Reid TD4618

This thread was discussed between 18/10/2020 and 19/10/2020

MG TD TF 1500 index

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