An oddity encountered while rewiring...

[Marshall V. Daut]

O.K. Progress is being made on this 1920 Touring's re-birthing, mostly concerning sorting out electrical issues that a previous owner blew off. A new or used horn switch seems to be the way to go to solve this past weekend's problem. See previous posting about that.

New problem encountered, although not a game killer. The wiring on this car was a rat's nest of old wires and needless add-ons. GONE!!! Back to basics. I have a couple wiring diagrams that agree with each other 95% of the time. I have been religiously following the connecting process for all three harnesses, real rocket science compared to rewiring a 1980 Corvette. I have done this several times over the years, so I had no fear going in on this one. After completing the re-wiring, the engine starts right up. Previous to the new wiring, it was a maybe-yes, maybe-no proposition. A prayer got the coils buzzing every other attempt. Anyway, that problem has seemingly been resolved.

However, when the lights are turned on, the ammeter goes into the positive side. I know, I know. Switch the wires around back there. I did that and the needle now goes into the discharge side of the ammeter when the lights are turned on. Why was it necessary to do that? The wires are routed correctly per the diagrams, yet when the yellow wire with black tracer is connected to the positive ammeter terminal per diagram, the needle goes the wrong way. I probably should leave well enough alone, but I'd like to get this thing wired correctly without resorting to cludgey wiring sidesteps.

Any ideas why this opposite polarity issue exists in this car?

Marshall

[Gen3AntiqueAuto]

Older ammeters show discharge to the right, maybe yours is labeled backwards from the original?

[Moxie26]

Could your battery be installed backwards with a positive ground ?

[Humblej]

Marshall,
It is not your wiring, your battery, or your car, it is your ammeter. So you have to reverse the wires on the ammeter.

[RajoRacer]

Are you using an original large Ford ammeter OR one of the small, imported ammeters used on Model As ???

[Marshall V. Daut]

Thanks for everyone's replies. I double checked the battery orientation today and it is correctly hooked up with the negative cable grounded to the frame. The ammeter is the smaller Model A style that has been glued inside the larger outer ring that originally held a larger Model T ammeter. Because I swapped the two wires on the back of the ammeter, do I also need to move the short wire connecting the back of the switch (marked "batt.") to the other ammeter terminal, contrary to how it is shown on wiring diagrams? Where should it go with this now-suspect ammeter?

An ammeter is a simple animal, designed to show current flow and draw: discharge = needle goes to the negative side, charge = needle goes to the positive side. That's pretty cut and dried. Why, then, would it be necessary to go counter to its natural tendency to show discharge when a power drain occurs for it show a charge? Were these foreign-made ammeters (and what ammeter produced for our antique cars in the last 50 years HASN'T been foreign-made?) built to work backwards? Or maybe because a Model A is a positive ground system, this ammeter was designed for Model A's and not T's with their negative ground electrical systems? That would be my guess.

Marshall

[RajoRacer]

It's the ammeter - all that are being reproduced are positive ground. You did what you needed to do swapping out the 2 wires on the meter - nothing else cares !

[TRDxB2]

This one of the best wiring diagrams. The J position on the ammeter is for the + positive connection to the BAT position on the ignition switch & the U is the - negative position on the ammeter from the cutout/VR on the generator via position 1 on the terminal block.

Some ammeters connections aren't marked so its up to the user to figure direction