Radar instillation 2000 PF, where's hot wire

[flycaster]

Going to install RD via using wires in overhead console. Have the wiring exposed, but need to know how to identify (preferably without using a meter/tester) which wires are either always hot, or become hot when the ignition is turned on (preferable method). Thanks,
Adam

[cyclone1410]

Originally Posted by flycaster

Going to install RD via using wires in overhead console. Have the wiring exposed, but need to know how to identify (preferably without using a meter/tester) which wires are either always hot, or become hot when the ignition is turned on (preferable method). Thanks,
Adam

Mate, the easiest and, really the only, way to be sure that a wire is "hot" is to use a tester or multimeter to test it. To have a guess or rely on someone elses wiring diagram is just asking for trouble, which could include burnt out wiring. You can buy a cheap meter at your local K-Mart or Tandy. Alternatively you can make up a simple tester using a 12V bulb and a couple of pieces of wire connected to it.

My Dad always said that if you are going to do something do it right the first time. BTW I am an electrican by trade.

[flycaster]

You are right. How about a quick 101 course in using a voltmeter to test for the ignition or always hot wire. I have a Radio Shack voltmeter and would like to know if the following procedure is OK. One lead goes into the 15v and the other lead goes into the DC-omega (resistance). Now the next part I'm too sure about. Which lead touches the wire and which touches the ground? Also, can I consider the metal housing as the ground? How do I use the meter to test for gound? Thanks,
Adam

[cyclone1410]

Originally Posted by flycaster

You are right. How about a quick 101 course in using a voltmeter to test for the ignition or always hot wire. I have a Radio Shack voltmeter and would like to know if the following procedure is OK. One lead goes into the 15v and the other lead goes into the DC-omega (resistance). Now the next part I'm too sure about. Which lead touches the wire and which touches the ground? Also, can I consider the metal housing as the ground? How do I use the meter to test for gound? Thanks,
Adam

OK. I will assume that the volmeter has two terminals on it. One should be marked as + or positive or in some cases just V and the other terminal should be marked as - or negative or in some cases Common.

Most cars these days are negative earth meaning that the frame of the car and consequently most of the metal bits are connected to the negative terminal of the battery. For the purposes of our test connect the -, negative, common terminal of the voltmeter to the frame of the car. This can be done by placing the copper part of the connecting wire under a mounting screw or preferable connecting a long wire from the negative terminal of the voltmeter to the negative terminal of the battery.

Test the operation of the voltmeter by connecting the +, positive terminal to the positive terminal of the battery. You should get a reading of something around 12V (sometimes a little higher - around 13V).

Now once that is done make sure the ignition key is off and connect the other terminal (positive, +, or V) of the voltmeter to each of the wires in the overhead console in turn and see if you get a reading from each. The reading, if the wire is 'hot' should be the same as the one you got doing the test above. Note which wires gave a reading and those that didn't.

To test for a wire that is only hot when the key is on, do basically the same thing as above but this time turn on the key and check each wire in turn and see which wires have different readings.

The procedure above is a little long winded however in most cases it will work fine. However is a few cases just because you get a reading off of a wire doesn't mean that is a direct power connection to the battery of the car as there could be other items in the circuit which can give a false reading. As I said though in most cases you should be OK.

I hope this is of assistance.

Regards

Craig

[flycaster]

I gave up the thought of hooking into the compass' wire as I didn't want to take a chance in screwing the compass up. Instead I opted to use a live wire that feeds the console lights. Although I gave up having the RD go on and off automatically, the hook up still works nicely. Thank for all your help.
Adam