T-Series Silly question on TD Grounding

[vping]

TD Question.
Just by looking under the bonnet (sans battery in the case of a TD), how can you tell if it is positive or negative? How would you know which went where? I don't think I stopped to look or check and I am having a dizzy made so this question came up.

 

[David_DuBois]

Vince all post war T series cars started life as positive ground, so if you want your car to be positive ground, wire it up as shown on the wiring diagram in the shop manual and you are good to go. After installing the battery (with the positive terminal going to ground), flash the generator to insure that it is going to put out a negative voltage (disconnect the wires from the generator, attach a jumper wire to the small terminal and quickly touch the other end of the wire to the negative terminal of the battery a couple of times). Check under the end cover of the fuel pump to insure that it doesn't have a diode installed in it and you are good to go. If you want your car to be negative ground, repeat the above steps, grounding the negative side of the battery and touching the jumper wire to the positive terminal to flash the generator. Revers the primary wire connections on the coil and reverse the connections to the ammeter. Again check the fuel pump for a diode and if it has on, insure that itis wired he correct way.
Cheers,

 

[Steve_S]

Dave has already answered your question so I'll just ask one thing. What does the dizzy have to do with what ground you're running? Nothing inside it cares about polarity!

 

[David_DuBois]

Steve - The distributor doesn't care what the polarity is, but the coil does. The direction the current flows through the coil determines the polarity of the pulse that it produces. For the best efficiency, the center electrode of the spark plug needs to be negative to take advantage of cathodic action of that electrode (electrons being boiled off as the result of the heat it is subjected to. In practice, having a pulse of the correct polarity will increase the efficiency of the plug by 10% to 15%. While this is not much of a gain, it is enough in some cases to prevent sporadic missing.
Cheers,

 

[Steve_S]

Indeed, but I interpreted his question as directly regarding the dizzy. Good information nonetheless.

 

[vping]

I have a spare TD dizzy that I sent to Jeff and he was going to set it up with Pertronix. He asked me if my car is positive or negative ground. I am not sure what to look for in the car. I did hook a battery up to it to start checking electrical but I hope I did not screw anything up. I was young and it was years ago.

 

[David_DuBois]

Sorry - the dizzy question just passed me by (thanks Steve for getting me back on track).

Vince - since you are having Jeff do your distributor (he did one for me recently and it's like having a new car)with the Pertronix ignition, you get to which ever polarity you want. In this day and age, there is no particular advantage of one over the other. The only reason to go with positive ground is strictly that it was original.
Cheers,

 

[Steve_S]

Agreed. If you plan to hook up modern accessories such as radio, GPS, etc then you may want to go with negative ground for simplicity's sake. If not, and you like originality, then positive ground will work equally as well.

If anyone else ever works on the car and you have positive ground, be sure to tell them about it. Even some British mechanics who aren't used to the earlier cars forget and connect things backwards.

I have all my cars as positive ground except for the GTS because it has EI. It's partly for originality, but also so they will all be the same because I don't want to have to think about it every time I work on a car. The GTS is the newcomer but I'm not changing five other cars just to match it!

 

[Matt_F]

Here's my two cents on an easy way to figure out how a car's wiring is grounded: look for the starter motor, then trace it back to the battery. That cable is the power to the starter, and the opposite will be the ground. It's fairly easy to trace the big, fat wire that's easy to see.

Matt

 

[vping]

That's true. I ordered my Dizzy set up for negative ground and will switch the car over. Having it as original as it is with negative ground won't kill me.

 

[Ed Kaler]

FWIW and for the "Planning Ahead Folder" /bcforum/images/%%GRAEMLIN_URL%%/devilgrin.gif InterState makes a battery that IS PLAIN black AND is offered in EITHER "post" configuration, /bcforum/images/%%GRAEMLIN_URL%%/angel.gif

/bcforum/images/%%GRAEMLIN_URL%%/cheers.gif

Ed

 

[vping]

Is that similar to a stock looking TD batery?

 

[Steve_S]

Westco battery, ala Miata. Tiny, very lightweight, zero maintenance, no battery acid and plenty of power for a TD.