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-   -   Can you tell where to tap on this harness? (http://www.jeepgarage.org/f73/can-you-tell-where-to-tap-on-this-harness-61104.html)

Dabitz 06-07-2013 09:00 AM

Can you tell where to tap on this harness?
 
1 Attachment(s)
My auto-dim, garage opener rear view mirror is aftermarket. I just got a new radar detector from Beltronics and would like to cut my old cable from old detector and tap directly into the vehicle. My rear-view mirror harness has 3 cables, one is black and white, the other two are black. I don't have a meter or anything like that to test voltages, etc., but I was wondering if it would be safe to assume the black and white is positive (left cable on picture)?, but not about the other two. Anyone with experience on this kind of thing? I guess I could try with my old detector first since I don't want to fry the new one.

Attachment 24777

Jim_in_PA 06-07-2013 09:07 AM

Re: Can you tell where to tap on this harness?
 
Don't assume anything...pick up an inexpensive meter from Radio Shack. Handy to have around anyway, and it will insure that you understand the true nature of those wires.

Dabitz 06-07-2013 09:12 AM

Re: Can you tell where to tap on this harness?
 
OK, I'll ask at Radio Shack what meter I need and how to use it.

Jim_in_PA 06-07-2013 10:17 AM

Re: Can you tell where to tap on this harness?
 
It's important not to guess...some gear doesn't have protection against reverse polarity and it's not a good idea to "smoke" something inadvertently. Once you have a meter, set it to DC voltage, attach the "black" lead to a known vehicle ground (you may or may not need to extend that lead to get to something directly attached to the car frame) and then use the "red" lead to test each of the connections on your harness. Do that both with the car completely turned off and with it turned on so you know if you have switched power and/or continuous power and on what lead(s).

Dabitz 06-07-2013 10:43 AM

Re: Can you tell where to tap on this harness?
 
Great, thanks again Jim. Will the meter tell which of the cables is a ground?

Richx76 06-07-2013 11:37 AM

Re: Can you tell where to tap on this harness?
 
Here you go... instructions to make your life easier.

https://learn.sparkfun.com/tutorials...e-a-multimeter

I'm not trying to be anything but helpful...just had a couple drinks is all.

the TL:DR of this is: Place the black lead of a multimeter set to DC voltage on a bare piece of metal on the vehicle or a known ground (screw head, etc). Use the red lead, and touch it to 1 wire at a time until 12 to 14 Volts DC is indicated on the meter. That is your positive lead.

To find the ground... Set the meter to "Ohms" (looks like the greek symbol for Omega) and again, leaving the black lead on a known ground... touch the red lead to 1 wire at a time until it reads "zero" Ohms. That is a good ground.

Repeat both processes with the vehicle power on/vehicle running. The reason? Modern transistor/logic circuitry in body control modules can simulate "ground" on a power supply circuity when the system is in a de-energized mode of operation.

Also... you can search the website Car Alarm, Car Stereo, Mobile Video, and Cruise Control Info for Installers (it's an audio installer site) for diagrams/information on your specific vehicle.

Good Luck!

Dabitz 06-07-2013 11:54 AM

Re: Can you tell where to tap on this harness?
 
Just when I thought I had learned everything I could possibly do on this forum. Thank you.

Dabitz 06-10-2013 09:35 AM

Re: Can you tell where to tap on this harness?
 
5 Attachment(s)
I know I feel like I cheated, but I went a different route and I'm pretty happy with the results. This I didn't want to give up the "smart" capabilities that my detector cable has. I routed the cable from behind the little compartment door at the bottom (cigarette lighter), behind the dash to on top of the dash where a small opening/cover is. I'm very happy with the results and it still allows me to unplug the cable on a very hot day, etc. You can see the opening where I pushed the cable through at the very top of the second picture below (behind the radio).

Attachment 24983
Attachment 24984
Attachment 24985
Attachment 24986
Attachment 24987

Thanks again everyone for the advice.

Richx76 06-10-2013 09:47 AM

Re: Can you tell where to tap on this harness?
 
I like it....good line of sight out the front. Plus, looks like that spot was designed for that cable :)

bigjgcfan 06-10-2013 10:01 PM

Re: Can you tell where to tap on this harness?
 
1 Attachment(s)
Just a thought...

But how about installing a nice rubber grommet to 'finish-off' the hole that you drilled in that opening cover?

Not only will it give it a custom look but it will also help with any vibration chafing on the power cord.

Dabitz 06-11-2013 09:30 AM

Re: Can you tell where to tap on this harness?
 
That's not a bad idea... It'll look more "professional". I will try to find those on my next trip to Home Depot.


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