Add a Tachometer

[ppronti]

Easy:

I 100% agree with you except I’m not sure what you mean by voltage may not be constant at the other end of a wire. But I do believe what I was trying to convey was the same idea. All components of a circuit including connectors, fuses, switches, buttons, and yes you are correct even about wire itself, etc… these things all have resistance, but for the most part, these resistances should be negligible values – if they aren’t negligible, there is a problem – corrosion or something.

If the individual reflects on their electricity class (or even a general introductory class in physics), V=IR (Voltage = Current (Amps) * Resistance (Ohm)). Voltage is a measure of electric potential, or a loss thereof when across a load. In an automotive (or likewise, motorbike) application, Voltage at the battery remains “constant.” Any automotive lamp/horn/speedometer/other load (in the GZ250 diagram we should be messing with) is rated for 12 V. If one is experienced with electrical systems of automobiles, motorcycles, etc., it is generally (if not absolutely) the case that most circuits have their respective loads (resistance) wired in parallel (for example, all lights should see the same battery voltage drop from one side of the load to the other). And automotive parts are generally built robust enough so that corrosion, and any potential-loss effects thereof, is minimized. So practically speaking, one generally should not need to check for small voltage drops in automotive applications, (with exception to finding out if there is corrosion or other circuit discontinuities) – which is why text lamps are available and so widely used – either there is 12 V potential available or there isn’t (an indicator light is on or off).

What does (more often than not) vary when we add/remove components in an automotive application is total current draw.

Any individual load requires a certain current draw. Since V=IR, and V remains constant (and most loads in automotive applications remain fairly constant), when you add a component (like our tachometer), you effectively reduce the value of R because you are adding a path for current to flow (if anyone wants to talk/understand this concept you can look up “parallel circuits” and the “effective/total resistance” thereof or ask here). So then the overall R goes down and thus the current draw goes up. Literally, every load in a parallel circuit requires a certain current draw.

[Water pipe analogy – it’s like taking a 6” pipe, cutting a section out of it, and using two 2” pipes to connect, the “resistance” would be seen at the 2” pipes. Adding another 2” pipe in PARALLEL would increase the amount of water (analogous to the amount of current draw in the electrical circuit) to flow.]

[The following is an example – they are not real numbers] If you have 5 lamps in your running lights system and each requires 1 A of current, total current draw for the five lamps is 5 amps. If we add our tachometer lamp circuit, in parallel (which is what I am offering suggestion to do), the total current draw for the running light circuit is 5.12 A because the tach light requires .12 A. (This current draw would be measured, in line/series, AFTER the “Ignition On” connection for the tach).

Anyway… probably boring people to death… and killing a lot of time… lol…