I will try to expose those who need it to basic ideas about electricity, and I encourage anyone to ask

questions, and I will try to clear up any misunderstanding.

First, a few basic electrical things. Electricity is measured by the following terms:

E = Voltage, expressed in Volts

I = Current, expressed in Amperes

R = Resistance, measured in Ohms

P = Power, measured in Watts.

These items are all interrelated in the following ways:

E = IR. In other words, Voltage is equal to Current times Resistance

I = E/R. In other words, Current is Voltage divided by Resistance

R = E/I. In other words, Resistance is Voltage divided by current.

P = EI. In other words, Power is Voltage times Current.

Power is also expressed as E squared, divided by R,

and also by I squared, times R.

So if one knows the value of two things, one can calculate other things without direct measurements.

In my humble opinion, everyone needs to have a multimeter. I have one in each of my vehicles,

more than one in my garage, and I have given away several. Harbor Freight has an inexpensive

unit which sells for various prices, from $15.00 down to $2.00, but also free with a coupon with any

purchase.

The Multimeter has several modes. Firstly, measuring Voltage, and it has several ranges. I recommend

always start with a higher range and then switch down to lower ranges as needed.

In the automotive world, Direct Current (DC) is for the most part 12 Volts but its not completely universal.

I have had vehicles that were 6 Volt and 24 Volts systems.

Also, generally speaking, the negative battery terminal will be the ground, or return, polarity. I had one

vehicle that was a positive ground system, but those are not seen much these days.

Another Voltage is the Alternating Current (AC) ranges. These won't be much use for most vehicles unless

you have some commercial vehicle or a Motorhome.

There are some Current ranges, but these will require inserting the meter into the middle of a circuit,

requiring some disassembly/reassembly. Mostly it will be easier to check voltages and calculate.

Resistance measurements will be very usefull, but care must be taken that there is no power on the

circuit before measurements, because a live circuit can fry your meter. It can be very handy to

check continuity in circuits when looking for a broken, or open circuit, and to verify continuity

where it is needed.

--->> Harbor Freight multimeter

https://www.harborfreight.com/7-function-digital-multimeter-63759.html