Sat/Navs and MG TD

I recently decided to try my Tom Tom Sat/Nav in my TD and of course straight away realised that the earth on the Sat/Nav is Negative and our TD/TFs are Positive earthed.

As TDs have a very convenient power take off, built into the dashboard, it seemed an easy proposition to utilize it.

The red (positive) and black (negative) dashboard sockets.

Assuming that the car has not had the polarity switched already, it’s a simple mod to make up a lead to switch the polarity from Positive to Negative for the purpose of using the Sat/Nav.

Check that the sockets on the dashboard are correctly wired i.e. Red is positive and Black is Negative, mine were incorrectly wired.

Purchase a Cigarette Lighter socket from Maplin and make up 2 leads of the appropriate length, I suggest one Red and the other Black and cover with black shrink sleeve.

Gauge of cable I chose was 8.75 amp 14/0.30.

Solder the Black lead to the central terminal on the Lighter socket.

Solder the Red lead to the terminal on the outer edge of the lighter socket.

Get hold of the correct brass Map Reader plug that was designed for our Dashboard sockets

Mark one of the terminals on the dashboard plug with Red paint and wire the Red lead to it.

The Black lead fits to the other brass terminal and is Negative.

I also made up a label to fit around the lead to remind me to make sure that Red is always fitted to Red socket on the dashboard in order to maintain the correct earth.

It may be possible to use other electronic devices in this manner however I have not tried any others, the output from our dynamos may be a restriction for electronics that draw more power.

Assuming that all the fittings are plastic then there should be no problems with shorting, however if its decide to make a secondary dash panel out of steel and mount the cigarette lighter socket, make sure that the appropriate fuses and insulation is used.

Readers may already have carried out this sort of modification and this may be old news.

For anyone thinking about this I hope that this short description is useful.

I am not an Auto Electrician and so must make the usual disclaimers, it’s up to the reader to carry out his/her own research and decide whether the equipment that is being modified is suitable.

Russell Dade

Ed’s note: Jonathan Goddard’s book Practical MG TD – Maintenance, Update & Innovation has a couple of pages on fitting a ‘12V Cigarette Lighter Power Socket’ and a couple more on ‘Satellite Navigation fitting’ (two alternatives).

Jonathan’s book, which has sold copies worldwide is available from the T-Shop for 6.99 GBP plus postage, or direct from the Editor at 85 Bath Road, Keynsham, BRISTOL BS31 1SR Tel: 0117 986 4224 e-mail jj(at)