hello everyone, new member here, can anyone tell me why my chassis voltage is sitting at 12 volts , vehicle stats and drives fine but  rear lights going haywire like with an earth fault . 

Measure the voltage between the battery negative post and the chassis, that will tell you whether you have a bad earth or not.Should be as close to zero as possible.

voltage is showing as about 12 volts , however I now believe this not to be the problem as i have festooned the car with additional earth wires to battery -ve and things revert to normal . I believe the voltage reading to be a floating voltage which did cause me much anguish. I now have to go round the earth points with copper grease , do you know where actual earth points for the rear lights is located?? thank you maccy this has been a good first visit for me. 

Don't use copper grease, it doesn't conduct well.

3 hours ago, bly54the said:

voltage is showing as about 12 volts , however I now believe this not to be the problem as i have festooned the car with additional earth wires to battery -ve and things revert to normal . I believe the voltage reading to be a floating voltage which did cause me much anguish. I now have to go round the earth points with copper grease , do you know where actual earth points for the rear lights is located?? thank you maccy this has been a good first visit for me. 

Most  modern DVM( meters) are very high impedance (i.e. they do not load the circuit )and will show the  no load  voltage( try putting a meter on the earth point showing 12v and then connect a load e.g. a brake lamp across the meter and i'd suggest voltage will drop) .  If ( with all the additional earths removed) and all rear lights switched off you get zero volts between chassis & the other point, try eliminating the circuit by looking for the light circuit which gives you a reading when operated. e.g. sidelights =no volts, but brake lights =a reading circa 12v, then it's most likely the earth for the brakelights ( most common suspect as they draw the most current and hence a greater voltage drop across any potential high resistance. )

Might be easiest to find the circuit that produces a voltage and run a wire from the earthy side of the circuit to chassis.

 

Edited 7 September, 20205 yr by VWD

thank you , sepulchrave , i will heed your advice re coppergrease . hello vwd  thank you also i am going to follow your suggestion using a conductor from the chassis to the brown connectors on the light clusters