Conversion from Positive Earth to Neg Ground ??

[George Zeck]

In process of upgrading / renewing my car. I've read a few items on the electrical conversion and it doesn't seem too difficult (in print). Just wondering if anybody out there has actually done the switch and has any words of wisdom.

Thinking of doing this so I can also upgrade the ignition system to a "Petronix" and of course in tandem -- changing plugs & wires.

PS -- I have a electical tach which I know will require "re-polarization" as well as generator and ignition.

Thanks all.

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[Steve]

There was a previous thread on this subject, on the MG forum, covered the subject in some depth too.

 

[George Zeck]

Thanks for that. For those interested:

https://www.mgaguru.com/mgtech/electric/et202.htm

it's for the MGA. Was hoping for some experience in the Spridget world (not that I really expect a huge difference) from guys who have undergone the task.

Tx-

Geo

 

[spritenut]

Re: Conversion from Positive Earth to Neg Ground ?

I have converted many Sprites to negative ground. Converted them all to alternators too.
basic + to - grd conversions consists of
1) switching the wires on the coil.
SW (or -) now goes to the distributor
CB (or +) now get the solid white wire from the switch

2) repolarize the generator.
Take a stout length of wire connected to the smaller field terminal on the generator and arc it on the + side of the battery a few times.

3) check the heater fan, it may blow backwards after converting, just swap the 2 wires at the motor.

4) TACH conversion.
Remove the tach from the dash, remove the bezel and glass.
remove the 2 screws from the back of the housing and the guts will drop out. on the back you will see a wire that is soldered to the power terminal. Right next to that wire/terminal there is a resistor.
Cut the wire, cut the end of the resistor.
Switch the 2 (resistor now goes to terminal, wire now goes where resistor was. resolder those 2 in their new spots.

Words of caution, if you have a later style elec fuel pump with a diode, it must be replaced. If it is a points only type, no mods are needed.
And only on one Sprite did my gas gauge work backwards after the conversion. I can't explain it, nobody else had this problem, and I had to change gauges to correct it.
Also be careful when arcing across a battery, watch your face, batterys can explode. This is best done outside on a windy day or if you have compressed air, blow around the battery area before arcing to remove any hydrogen gas around the battery. Not likely but I have heard of batterys exploding when jumpers are hooked to them.

 

[screenprinter]

Re: Conversion from Positive Earth to Neg Ground ?

One other little tip that I learned early on - If you run the auto after the conversion without disconnecting the positive ground tach it'll fry the little guy - When I bought my Sprite from a Foreign guy who ran a used car lot he couldn't figure out why he couldn't get it started - When I looked under the bonnet there was a clear legend "Positive Earth" yet the battery was hooked up Negative Earth - Car won't run too well like that - Fortunately the only side effect of this was the fried tach.
Being a "leave it like it came from the factory" nut and being indifferent to radios in convertible sports cars I hooked it back up Positive Ground - She rolled over about 4 times, caught and purred like a Singer Sewing machine - Nysonger repaired the Positive Tach and I was back in business.

Bob M.