I hate wiring. It's all Greek to me. I can replace existing wiring or components without issue but adding or changing tends to throw me off and i try to avoid it as much as possible.

I am wanting to hardwire my GPS to my rear view mirror wiring harness. I have the XLT poverty package so nothing really fancy in the rearview aside from the autodim feature. I don't use the auto dim feature as I have a clip on wideview and childview mirror.

I plan to unhook the harness from the mirror and tap the harness using this little bugger.
I am pretty sure the rearview is ignition power or else it would be functioning when the car is turned off which would be pointless.
I have yet to find the wiring diagram.
So I need to use the multimeter to find the ground and the 12v power.

I have 5 wires:
Brown
Black
light blue
light blue/grey
light blue/brown

I have a 2016 and the only wiring info I have located is for a 2018 with all sorts of options in the mirror. The only common color is black and that is the ground.
I am going to presume that the brown is the ignition 12v wire. But would like to be sure before I just go plugging things in and be wrong and pop some fuses.

So using my multimeter how do I go about determine which is ground and which is 12v?

Dumb question I know.

Find a good ground anywhere on the vehicle. Set your multimeter to ohms. With one probe on the ground, use the other to check each of the 5 wires. When the multimeter reads 0.00+/-, you have found your ground wire.

Then can put the multimeter on DC volts, and with one probe in your new ground, can find the hot wire with the key on, on the other 4 wires.

Hope that makes sense, and good luck!

Set meter to V 12>
Turn on key
Touch black meter wire to a ground point on the vehicle
Touch red meter wire to metal contact at the end of the brown wire,

if it reads 12v then you have power, switch off key while you have meter hooked up and see if meter returns to zero.

Ground (black prob) of the meter to truck body (anything unpainted) then check each wire from mirror for 12 volts.

The setting may be something like 20v DC, just not AC.

Test it on the battery to see how it will read.

What make/model is your meter?

First, you need to determine how much current your GPS draws, because it may not be advisable to connect it to the mirror. This info should be available in the owner’s manual, and the size fuse that comes inline with the power cable should also provide a clue. If it’s over 1 amp, I would advise against tying into the mirror wiring.

As to how to determine positive voltage and ground, start by connecting your meter’s ground lead to a known ground, such as the outside of a cigarette lighter receptacle, or any metal in the door jamb or under the dash that is connected to the vehicle chassis. Then probe each wire to find one that reads 12 volts (or close). Turn ignition on and off to verify that this wire is only energized with ignition on.

Your meter should have a continuity function, that will make an audible beep when the two leads are in contact. Using the same ground you used to test for voltage, test the other wires to see if one is showing continuity to ground. If you find one that appears to be a good ground, check it with ignition on and off, and with your headlights on and off, to make sure it continues to show ground. It is common for light wires to show ground until the lights are turned on, and then they change to positive voltage.

Lastly, once you have found a ground in the harness, test it for positive voltage with ignition on and off, and lights in and off. A true ground will stay at ground and show no voltage.

A regular Test Light with a sharp point (ice pick thing with a light bulb and alligator clip) is the best tool for finding your Switched Hot, fwiw. Way less fiddly, more obvious when it finds a hot wire, and the sharp point will more easily fit into molex plugs or pierce the insulation on a given wire.

I love Multi Meters but never bother using one for this task.

Try blue/brown as 12v and black/yellow as ground

quote:

First, you need to determine how much current your GPS draws, because it may not be advisable to connect it to the mirror.

Sorry, I left the link out of the original thread. I will be using an adapter with the proper thingamajig regulator for rear view mirror power to Dashcam/GPS units.

Two-prong Universal Dashcam Adapter (12V to MicroUSB) https://www.amazon.com/dp/B07B...cp_api_NZD6BbBC3BBHX

I have a Craftsman 82140 multimeter.

I have the black probe connected to the com port and the red probe to the V*Ohms*mA port.
Have the dial set to VDC200
I have the black probe to the door hinge
I put the red probe to each wire and get nothing but 0.00

quote:

I have the black probe connected to the com port and the red probe to the V*Ohms*mA port.
Have the dial set to VDC200
I have the black probe to the door hinge
I put the red probe to each wire and get nothing but 0.00

What does your meter read if you connect it to the vehicle battery?
If there is no reading then, try switching to the 20VDC scale.
Still no reading, a defective meter lead.
If it reads, likely the ground connection on the door hinge is not good enough.

Ignition on?

quote:

Originally posted by Black92LX:

quote:

First, you need to determine how much current your GPS draws, because it may not be advisable to connect it to the mirror.

Sorry, I left the link out of the original thread. I will be using an adapter with the proper thingamajig regulator for rear view mirror power to Dashcam/GPS units.

Two-prong Universal Dashcam Adapter (12V to MicroUSB) https://www.amazon.com/dp/B07B...cp_api_NZD6BbBC3BBHX

I have a Craftsman 82140 multimeter.

I have the black probe connected to the com port and the red probe to the V*Ohms*mA port.
Have the dial set to VDC200
I have the black probe to the door hinge
I put the red probe to each wire and get nothing but 0.00

That harness you linked does NOT negate the need to find out how much current the GPS draws. I would advise not to use that if the GPS draws more than 1 amp of current.

You need to make sure the black (ground) probe is attached to a good chassis ground. Door hinge only if you've scraped through the paint. On most vehicles the post that the doors latches onto is bare metal and usually it is a good ground. Learn how to check continuity to determine if you have a good ground. Use the outside of the cigarette lighter socket--the part where the outside of a plug contacts--not the center conductor which is at the bottom in the middle.

quote:

Originally posted by 46and2:
A regular Test Light with a sharp point (ice pick thing with a light bulb and alligator clip) is the best tool for finding your Switched Hot, fwiw. Way less fiddly, more obvious when it finds a hot wire, and the sharp point will more easily fit into molex plugs or pierce the insulation on a given wire.

I love Multi Meters but never bother using one for this task.

This is VERY BAD advice for any semi-modern vehicle. A test light with an alligator ground clip provides ground to whatever you are probing, and absolutely can fry electronic circuits, deploy airbags, and destroy computer circuits in modern vehicles. Good multimeters are isolated and won't cause these problems.

There are modern "test lights" that actually have a circuit board built in, but the old standard test light SHOULD NOT be used to probe anything in a modern vehicle.

Black, I just sent you an email with my cell number. Call anytime, but leave a message if I don't answer and I'll call you back.

quote:

Originally posted by honestlou:

quote:

Originally posted by 46and2:
A regular Test Light with a sharp point (ice pick thing with a light bulb and alligator clip) is the best tool for finding your Switched Hot, fwiw. Way less fiddly, more obvious when it finds a hot wire, and the sharp point will more easily fit into molex plugs or pierce the insulation on a given wire.

I love Multi Meters but never bother using one for this task.

This is VERY BAD advice for any semi-modern vehicle. A test light with an alligator ground clip provides ground to whatever you are probing, and absolutely can fry electronic circuits, deploy airbags, and destroy computer circuits in modern vehicles. Good multimeters are isolated and won't cause these problems.

There are modern "test lights" that actually have a circuit board built in, but the old standard test light SHOULD NOT be used to probe anything in a modern vehicle.

^^^
This.

The sharp point of a test light is handy to pierce insulation or backprobe a molex type connector. Find a way to back probe the connector or pierce the insulation with your DMM instead.

GPS hardly draws anything. Probably way less than an amp. I’d have no problem using the mirror power. I’d leave the mirror hooked up and functional. Use a tap to hook up the wiring. Tap into the 12v switched line that you want.

With all the work you do on your rides, why not buy a subscription to the consumer versions of AllData or Mitchell On-Demand and get everything in the shop manuals? Including, in this case, wiring diagrams.

See if this helps. https://www.f150forum.com/f118...head-console-390476/

One thing of note is using the Volt-Ohm meter. You should always check for volts, then ohms.

Each wire in the harness is gauged for a certain load at a prespecified temperature. The ground wire is designed for the total load of the circuit at full load. If it were me, I would run the wires for the GPS from the right side of the mirror, down the passenger side A-pillar (toward the inner side of the curtain airbag assembly if so equipped) to the fusebox located behind the kick panel. The (30amp) fuse for the heated seats will be there even if your ride was not equipped for them. This is where you would be better served for powering your GPS.

Drawing power from this would allow you to have the GPS to be powered while the truck is on. Modern Fords usually have RAP (retained accessory power, meaning power will be on until you turn your truck off and then open the door) so it will say on with the radio. This comes in handy if your GPS has bluetooth for your phone or an FM transmitter to the radio. Be sure to add the proper fuse here.

One other thing of note: Most GPS units will have a built in antennae as part of the power cord to receive data from up to seven satellites. Check with your GPS manufacturer to see if this is so. I don't know of any that have an internal antenna only, but wouldn't rule this out. If you run the wire closer to the windshield from the headliner and down the A-pillar trim, it should get better reception.

I hope this helps. Good luck.