Could you confirm that in Mark IV a plus (not a minus as in modern vehicles) is connected with the body?
Yes, all MKIV’s and all MKV’s were positive ground! 
Cheers!
Here is the wiring diagram.
Zoom it in and you can see a very tiny + on the grounded (earthed) battery terminal.
The question comes up quite often on these forums for the early cars.
Lucas believed there were two advantages to positive ground.
- less erosion from spark at the spark plug and distributor rotor
- less corrosion at the battery terminals
They published their conclusions in a Correspondence Course for dealer’s technicians.
The main reason people switch to negative ground is to run modern electronics such as an alternator, transistor radio or other mobile devices.
1 Like
Thank you very much for all details!
What are your advice on installing an alternator? I am considering this solution. I am afraid that in the case of using a traditional generator/dynamo, I will have to deal with constant power shortages.
My standard generator in my 120 has been working fine for 30 years after I cleaned the commutators and install new brushes. Also cleaned the voltage regulator contacts. Same with my '38 SS, cleaned everything and working fine for 3 years.
1 Like
Unless very unusual circumstances of driving or more power consumption items are added beyond the original car design, a correctly-functioning generator is adequate. I’ve never wished to have an alternator in a car originally supplied with a generator. My 25 years of Mark V driving have all been with a generator.
1 Like
I agree. If you are worried about capacity then change to LED lighting and that will give you a lot more scope.
Peter
Thanks a lot @Rob_Reilly @Roger_McWilliams @Peter_Scott !
Your support is much appreciated. Let’s keep original. I stay with generator.
Agreed: if fitted with the electric stuff that an early car had, a well-tuned generator should suffice.