Test light

Hello, automotive test lights are only used on 12 volt circuits, do not use it at home. Houses are 110 volt, you will burn the test light out, and probably get a shock. Testing a car, you need to touch the bare wire or the end of a connector . If there's insulation on the wire it won't read. You can use an amp clamp around a wire to measure current flow because it reads the magnetic field on the wire.

So I have to strip the wire to use the test light on it.

Do I need to have the car on to use the test light to test ground and electrical connections?

No you don't need to strip any wires bare, you don't want to do that because it will then be exposed to moisture in the future. When testing a wire, go to a connector and back probe it with a t-pin if possible. When testing a circuit for just general power, test light connected to battery negative, key on so power is present. Now depending on what you testing, such as a head light bulb, it's best to have the car running so the circuit is loaded. Meaning current is flowing and if there is a problem. It will reveal it's self when the circuit is loaded or under stress. If you want to test a ground circuit, test light connected to battery positive, same idea. Back probe a connector your testing and the test light should light up bright. These are the very basics of testing automotive electrical circuits. A multi-meter can be used in the same way to get an accurate reading of voltage on any circuit. Any other questions I'll be happy to try and explain in the simplest terms.

Here are a couple articles to help you understand the basics a bit more:

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

https://www.2carpros.com/articles/how-to-check-wiring

https://www.2carpros.com/articles/how-to-use-a-voltmeter

I'm installing a new radio into my vehicle and I want the steering wheel controls to work also. I just want to check which wires are the steering wheel controls so I can set them them up with my new radio's harness. So I should just follow the cables to the harness and use the test light their at the harness.

Okay, does this car have an amplifier for the audio system? and are you replacing the stereo with a factory radio or is it after market?

Here is a wiring diagram of a system with an amplifier. Even though both systems with or without still use this Dark Blue wire for control from the steering wheel. Different voltage signals come from the steering wheel on this same wire, going to the radio to tell it which command signal was sent.

Can I use the splicer below to connect the dark blue steering control wire with the wire from my aftermarket radio to create the connection?

You have to make sure the new radio can except the voltage signals coming from the steering wheel controls. That's why I was asking if the new radio was aftermarket or not. If you notice on the second wiring diagram, the dark blue wire runs threw the front airbag module. So I wouldn't be hooking up aftermarket components to this circuit. You don't want to set the airbag off because of sending the wrong voltage threw that module.

How do I determine if the aftermarket radio can accept the voltage signals of the steering wheel controls?

It's built into the stock radio, that's why the steering wheel controls might not work with an aftermarket radio. These are different voltages that come in on that one wire and the radio interprets the voltage reading correctly to change settings, such as volume levels, seek and scan, am/FM. You could try calling the dealership and see if they have a solution to this, but be careful just hooking up wires like this. You can cause more problems than it solves.