Classic cars forum & vehicle restoration.

Ray White · Joined: 02 Dec 2014 Posts: 6303 Location: Derby

Probably something I should know but just can't remember...

Should earth wires in a positive earth car be red?

Bitumen Boy · Posted: Sat Aug 24, 2019 5:45 am Post subject:

I doubt it. My Herald was originally positive earth but all the earth wires are black, and the colour coding in the loom seems to follow the general conventions of the time. Of course there's always an oddball..!

ukdave2002 · Joined: 23 Nov 2007 Posts: 4104 Location: South Cheshire

Hi Ray

In the UK from the early 30's most vehicle manufactures adopted the Lucas standard in which all earth wires are black, regardless of vehicle polarity, certainly all vehicles in the Nuffield/ BMC group used this convention Smile

Dave

Ray White · Joined: 02 Dec 2014 Posts: 6303 Location: Derby

Thanks guys. I shall be completely rewiring my MG TC which is positive earth. At least I now know for sure that earth wires are black regardless of polarity.

The confusion came about because I was looking at the colour of battery cables. It seemed counter intuitive for a red wire to be connected up to a negative terminal. Confused

ukdave2002 · Joined: 23 Nov 2007 Posts: 4104 Location: South Cheshire

Ray

My 57 MGA is 12v positive earth with 2 x 6v batteries fitted. From the factory all the battery cables had black insulation including the starter cable, the only exception is the positive battery to chassis (earth) which was a plain braided cable.

Dave

Ray White · Joined: 02 Dec 2014 Posts: 6303 Location: Derby

ukdave2002 · Joined: 23 Nov 2007 Posts: 4104 Location: South Cheshire

Ray

Coincidentally I fitted an electronic ignition distributor and a Stealth dynamator to the MGA when I restored it.

Unfortunately I had a parasitic current draw problem that would leave the battery flat after a couple of weeks if the car wasn't used, this was traced to the dynamator which was out of warranty (note to self don't buy these things until you need them!)

To stop the battery drain I fitted a relay that isolates the dynamo when the ignition is off; this was supposed to be a temporary fix some 4 years ago! The problem will almost certainly be a leaky diode in the units rectifier that wont take long or cost much to fix, your post reminded me its another job on the list!

Dave

Ray White · Joined: 02 Dec 2014 Posts: 6303 Location: Derby

As it happens, a relay came with the Dynamater.

I haven't yet read all the blurb but will be more cautious having read about your experiences with one of these things!