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MG TD TF 1500 - Converting to Negative earth

I've been fighting this change for 10 years. For those that have done it, I'm sure it was simple, but I am thoroughly intimidated for fear of blowing up my generator or having my starter start my engine running backwards??.

I drive my TF a lot - typical summer season = 6,000 miles or more. The reality is, that I want to convert to an alternator, and install LEDs wherever practical. (not hard to see why I have over 350,000 miles on it)

Can someone point me to a good article that covers all the bases. "Flashing the generator" for instance, sounds like a scary and gross over-simplification!


Gord Clark
Rockburn, Qué.

Gord Clark


The man you want to speak with is Dave DeBois. I think he has instructions on his website.

As I recall from my TF it's rather simple.

Reverse the amp gauge wiring, and re-polarize the gen and regulator. I think the fuel pump could be an issue if you are still using the old style.

I'm sure Dave will offer his assistance as soon as he reads this.

Dan Nordstrom

Good thought - thanks.

Gord Clark


Here you go.

S Grimm


Many thanks. I couldn't find it. However it raises some other questions. I'm a (retired ) electrical engineer, but this is way beyond me. There's a chap up the road who did it to his Singer, so I'm going to consult with him.

Looks like I'll have to change my pertronix, too.

I'm really spooked.

Thanks all.

Gord Clark
Gord Clark

Don't forget the most important part.......reversing the battery connections. :)
Dan Nordstrom

Gord - "Looks like I'll have to change my Pertronix, too."
Yes, you will have to get a new, negative ground Pertronix, the rest of it is just following the steps in my write up - you shouldn't have any problems. Cheers - Dave
DW DuBois

Gord, did this years ago to my TF and TR4-A, don't remember the process but is was relatively painless. Will also change the YB when I get to that point.
Hope you are well. Larry
Larry Brown

Why change now Gord? Putting in a boom box? :-)
L E D LaVerne


If you're going to an alternator why worry about "flashing" anything? Remove your generator, bypass your regulator, swap battery and alternator, replace Pertronix and you're done.

Gene Gillam

Gene, don't forget about changing the ammeter wiring, the coil connections, and (possibly) the fuel pump (if it is still polarity sensitive.

Electric clock?
D mckellar

Is there an alternator that has a tach drive feature? What about the pulley size?
John Quilter

Lew3 - I need to learn o proofread...that second alternator was supposed to be 'ammeter' and yes, I did forget the coil. 8^)

Gene Gillam

The clock is not polarity sensitive.

Mr. Gord Clark. Good day to you and others.
If you have installed Mr. DW Du Bois's
brake light relay,you have to change that
I think that is polarity sensitive ior?
Thoralf. NORWAY TD 4490
Thoralf Sorensen (TD4490)

This thread was discussed between 22/06/2016 and 23/06/2016

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