31 replies to this topic

[Gr4h4m]

Hi all I have been searching all over the forum for a how to guide to convert to Positive to Negative earth.

I have the basic's

- re-wire the rev counter
- re-wire the batt
- re-wire the coil switch the + and -
- Flash the dynamo (Not sure of what leads to where)
- the Lucas regulator (I'm not sure what need to be done here, I have only read about changes when using an alternator and I want to stay with the dynamo)

anything else? anyone know about the dynamo / regulator?

thanks

[Bounce]

Why would you want to??

[dklawson]

The main reason I would consider making the polarity swap is that it's virtually unheard of for people today to have a positive ground car. It's quaint, it's original, but if you ever are stranded by the side of the road and someone offers to jump start your car it's a technical point that's often overlooked in the frustration of having a broken down car. The results can be bad. If you're not after a concours restoration, switch to negative ground for safety and convenience.

As for polarizing the generator, see:
http://www.mg-tri-jag.net/tech1.htm
and
http://www.minimania...81/ArticleV.cfm

The regulator (control box) should not require changing or anything. Some people take this opportunity to clean them and dress the points in them with a bit of sandpaper but that's about it.

[Gr4h4m]

thanks Doug L

[Dan]

Why are you keen to stick with the dynamo Gr4h4m?

Also, got a stereo? You'll need to change that too.

[Gr4h4m]

Why are you keen to stick with the dynamo Gr4h4m?

Also, got a stereo? You'll need to change that too.

Dan I'm sicking with it for an authentic look, plus I have never had any issues. I dont have anything in the car thats + earth except the rev counter which will run either + or - earth.



I do have a couple of questions:

- My coil had more than 2 wires that were in the instructions. Do I switch everything over so all of the wires that were on the - side to the plus and vice versa?

- when you flash the dynamo without the belt on should it spin? I cleaned up a section of the case and attached the negative then touched the + to the smallest terminal for 3 secs 3 times, but it didn't spin

Thanks for any help

[dklawson]

I have not flashed a generator so I'm not sure how they are supposed to behave when this is done. However, generators will "motor" if you feed power back into them so I assume what you're describing would be normal.

The early coils had terminals marked SW (for ignition SWitch) and CB (for Contact Breaker). These coils were for cars built for positive ground. When you switch to negative ground, anything that was on SW would be moved to CB and vise-versa. It's not uncommon to have two wires on each coil terminal. If your car has an electric fuel pump, there will be two wires on the side of the coil connected to the ignition switch. These are typically white wires and they still need to be on the side of the coil connected to the switch. The other coil terminal typically had a single white/black wire that went to the points in the dizzy. Later cars with voltage sensing tachs sometimes have a second white/black wire on that coil terminal. Presumably that's your situation since you said your tach will work with either ground. The early Smiths tachs (RVI type) which would have been in service when positive ground cars were built require more complicated wiring and require modification to work on negative ground. If this paragraph doesn't address your wiring questions perhaps you can post a picture of what you have.

[Gr4h4m]

I have not flashed a generator so I'm not sure how they are supposed to behave when this is done. However, generators will "motor" if you feed power back into them so I assume what you're describing would be normal.

The early coils had terminals marked SW (for ignition SWitch) and CB (for Contact Breaker). These coils were for cars built for positive ground. When you switch to negative ground, anything that was on SW would be moved to CB and vise-versa. It's not uncommon to have two wires on each coil terminal. If your car has an electric fuel pump, there will be two wires on the side of the coil connected to the ignition switch. These are typically white wires and they still need to be on the side of the coil connected to the switch. The other coil terminal typically had a single white/black wire that went to the points in the dizzy. Later cars with voltage sensing tachs sometimes have a second white/black wire on that coil terminal. Presumably that's your situation since you said your tach will work with either ground. The early Smiths tachs (RVI type) which would have been in service when positive ground cars were built require more complicated wiring and require modification to work on negative ground. If this paragraph doesn't address your wiring questions perhaps you can post a picture of what you have.

I had a black wire, (White/black goes to the dizzy) and white/brown wire. Plus the wire for the tacho I have switched everything over which I think seems correct with your post.

[Dan]

I know they are expensive, but have you seen these?

[dklawson]

You know Dan, I still have the PM you sent me several years ago with the link to that site. I even inquired about getting one shipped to the U.S. Even before the dollar tanked this was a very expensive thing to consider in the U.S. Moss does not support the Mini in the U.S. but if I wanted one of those Dynalites I was going to have to have Moss U.S. order it for me (as a special order through the group that handles Sprites and Midgets). At the time it was going to be close to $800 delivered. I decided originality wasn't worth that much to me.

[Gr4h4m]

I know they are expensive, but have you seen these?

yep they look great but I'm with DKLawson... too expensive for the miles I do + I don't need to change the regulator

Edited by Gr4h4m, 22 March 2008 - 06:52 PM.

[Gr4h4m]

do I need to swap the elec fuel pump leads?

[dklawson]

I don't know enough about the electric SU pumps used on the Mini to give you a simple answer... you are talking SU aren't you?

If you have a Facet or other electrical pump then YES you have to swap the leads.

If you are talking about an SU pump, some of them (over the years) have had capacitors or diodes wired underneath the black Bakelite cap on the pump. Their job is to reduce arcing of the fuel pump points. If you remove the cover and find a diode, unsolder it, reverse its direction, and solder it back in place. If you remove the Bakelite cover and find a capacitor, no change is necessary. If you can't tell the difference between a diode and a capacitor, treat it like it's a diode and solder the component in in the other direction. If you find nothing there... great. Regardless, you don't switch the pump's wiring, you only switch the internal diode direction if you find one. (Switching the capacitor direction isn't necessary but won't hurt if you do switch it) .

[Gr4h4m]

yep its an SU but I think its had its day (38 years old) I think I will swap to a facet.

[Dan]

If you're after originality then why not go for an SU pump overhaul kit which include electronics to replace the points? You'll have a much more reliable pump that still looks original, after all SU pumps are rebuildable.