MTFCA Forum

With my current WWI ambulance project, I have lights, horn, a siren, and a interior red lamp for the interior ambulance bed. So, I would like to install some junction blocks, not terminal blocks to run positive power through a fuse to a junction block with about 6 posts. And, a seperate 6 post unction block that I can run one wire direct to the negative on the battery and not worry about grounds.
I could do it under the hood, but plenty of room under my wooden cowl and dash to hide it all. I would use cloth covered wires, so any that are seen would look period correct. My 6v battery is being mounted in the drivers side tool box on the running board and I could even install the blocks and all wiring connections inside that large tool box and be totally out of sight. Short run from battery to junction blocks that way.

Before purchasing blocks, I'm seeing descriptions that mention 12v but I'm not siing how a brass strip with screws would be voltage specific.
Any electrical auto guys out there that can guide me as to what to acquire for this? I would run all the accessories directly off the battery and not go through key ignition, magneto, or even the amp gauge, although I could go through the amp gauge to measure draw. Headlights would probably be wired OE through light switch and amp meter, but all other toys wired with the power distribution blocks.

I'll hang up and listen.

Robert,

You'll need to determine the amperage draw on EACH item you plan to power as you planned above. Let's just say it's 25 amps. The horn and siren will, most likely, draw the most power. Once you have the total expected amp draw, ADD a minimum of 25% as a safety margin. Knowing the amperage of each device will allow you to choose the appropriate size wire for that device, with lights using smaller wire and the siren using the largest wire.

Next, you will need to choose the size of the block you wish to use. The voltage rating is NOT important but the amperage rating IS. One reason "progress" moved from 6 volt to 12 volt systems is based on amperage. Avoiding all the nitty gritty formulas, it is a good idea to figure a 12 volt system will have one half the amperage of a 6 volt system as far as CAPACITY is concerned. Thus, wires in a 12 volt system can be smaller for the accessory. Ensure the blocks you choose are SAFELY capable of handling the amperage you figured earlier. Remember: As voltage goes up, amperage goes down for a fixed arrangement of loads. AND, as voltage goes down, amperage goes up for the same fixed loads.

We all know that something rated at 6 volts will work on 12 volts, just not for very long. A 12 volt accessory will work on 6 volts, just not as fast, loud, or bright. It all comes down to Volts, Amps, and Resistance.

Your idea of having a Positive block and a negative / ground block is a good one as you can put them each in any convenient location and run one larger wire to the battery for each.

I highly recommend a battery disconnect switch. Again, ensure a switch with greater amp rating than you think you will ever need. Include fuses for automatic protection. Most will recommend the disconnect switch be placed in the ground to the battery. I DISAGREE with that location. WHY? Because the battery positive is still connected to the vehicle. I prefer to mount the switch in the POSITIVE leg to ensure the battery is not able to make a path to ground in any way.

Good Luck

Battery cut off is great reminder. I have a fuel shut off, so why not the power as well to prevent battery drains and accidental start ups at display events. I usually use the ones that install right on the battery terminal and use a round plastic key that can be removed and taken with me. Once inserted, it completes the ground.
Thanks for the math homework, but it will help with draw and fuses for the amps. I have seen power distribution set ups with modern U fuses for modern cars, and could hide one of these in the tool box with the battery.