6 & 12 volt Ammeters & Ignition Switches

[Guest DBAcadia]

Hi All; I have two related questions. Are ammeters and ignition switches

voltage specific? I know the 6volt ammeters read 20-20 and 12volt 12-12.

Q: can one use 12-12(12volt) ammeter in 6-volt system without burning up

the ammeter or worse?

Also,I have what I know is 3-way DB ignition switch used on 12v '24, front

mounted to dash used w/o cowl lamps, and a 3-way which fits same 3-screw

hole but mounts from behind dash much like '26 6v but I don't think is DB.

Q: Can I run cowl lamps (6v) and headlamps (6v) safely together on a 3-way

switch originally built for 12v w/o cowl lamps, and if so should I use the

older DB switch or if it doesn't matter is it o.k to use the unknown switch

which looks more correct?

This is for the '27 sedan that became speedster.

[Guest DodgeKCL]

Neat Dodge. I've been rebuilding a light van that looks very much like your car and is 'coach built' as well.

Ammeters are not voltage specific. The reason the 6 volter has a higher current reading is because a specific load ,such as lights, will use TWICE the current on 6 volts as it would on 12 volts. (But you can't just switch 6 and 12 volt devices back and forth as they are designed for the specific voltage.)

Also charging a 6 volt battery and running a 6 volt car while driving would show more current on a 6 volt car's ammeter.

You also have to use wire that is basically 2X as thick as 12 volt wire because it will have to allow 2X the current flow during it's life time on 6 as on 12 volt wiring.

DO NOT use 'modern' battery cables meant for 12 volt systems on your car as they will not pass the current needed on a 6 volt system and you will get 'hard starts' even in the Summer. Curiously a 12 volt wiring loom will pass enough current over a long drive to recharge a 6 volt battery but only to have the 12 volt BATTERY cables refuse to pass enough current to crank over the engine fast enough for a 'smart' start. Making for much head scratching by many owners of vintage vehicles on many of these car sites.

Ohm's Law.

Theoretically the 12 volt switch would not be built with enough 'brass' to pass the required current for 6 volts. However, like ammeters, switches are not particularly current sensitive. I've used various makes and models for various purposes over 50 years and not had any problems. I would hook up the 12 volt switch with the 6 volt expected loads and leave it running on a bench for a few hours. But be warned that it is my experience that these old switches get warm even when they're original equipment in an original car. My '33 headlight switch gets warm in use and I can feel the heat when I reach home and touch the knob to switch off.And yes I've disassembled the switch and polished the contacts to no avail.

[Guest DBAcadia]

Thanks KCL for the info. I do understand the need for the thicker wire. The car is 6volt

original and I'm keeping it that way. The original heavy starter cables all work fine and

I cleaned all the contact ends. Do you have insight to the second (and) third question?

The unknown ignition switch may or may not be 6volt. Either way it is 3-way also, not

designed with the PARK (cowl lamp) setting. Is it too much load to wire the cowl lamp

wires to the ON (headlamp) contacts ? I've got a feeling it would be or all switches

would be 3-way. Maybe I should put the cowl lamps on a toggle as there is an extra

hole in the dash.