Wiring/electrical expert opinions.

[jjstang 51]

Rewiring the car. Now all the grounding places under/around the dash are covered or hard to get to. I was thinking of running a single wire to attach all the ground wires to, then grounding it somewhere significant at the end or both ends. Is there a good reason not to do this. Would 10g wire be sufficient. Thanks 

[69NC 21]

I would not recommend running a ground wire to all the different ground wires in the harness and then running that one wire to ground as it is likely to increase the resistance and therefore potentially introduce noise or have some of the circuits ground reference float. This could for example mess with a digital fuel gauge.  This is why for digital signals they run a separate ground reference that does not carry any significant current load. another example of running a separate ground wire back to the battery for a single device, like an amplifier would be to help reduce noise as that one wire only has the current from the amp flowing on it. But again this one circuit, not a bunch of different circuits lumped together.

 The chassis is a excellent ground point with near infinite capacity.

 

Form a theoretical view on pure electron flow (or hole migration for the physicist) if you have a connection to a ground point that will work. The theory is in a perfect environment with zero ohm connections and perfect conductors. Nothing like the real world.

Great question!

 

[det0326 179]

If u are running this ground plane for stock things such as lights, motors etc it is a great idea. I did on my car and eliminated the problems of things not being grounded sufficiently because of new paint and other reasons.

[Mach1 Driver 560]

I have some sections of a post I wrote that refers specifically to grounds, but it would help to know if you have a tach or not. The dash pad and instrument cluster can easily be removed in less than an hour for access to the dash ground wires. In particular I'm thinking of wire 57 black which is below the cluster with access only from the top.

[Vicfreg 771]

69NC has a very good point.

I did a AAW wiring kit and ran a separate ground wire from under the dash back to the battery (trunk mounted) for all my digital stuff (VHX dash, EFI, digital ignition, audio, Vintage Air controller, PWM controller, etc.)   I installed a grounding terminal block under the dash, for this. I also installed a similar grounding terminal block in the trunk for stuff I had mounted back there.

I grounded my battery to the rear frame rail, using a huge ground cable.  I also grounded my engine block at the starter, to the front frame rail with the same cable.   The AAW under dash wiring is grounded to the metal dash/firewall. Everything works great.

.pdf attached with my grounding diagram. Pics of trunk and under dash grounding terminal blocks attached.

Mustang Grounding Diagram.pdf

[jjstang 51]

A electric engineer I’m not. 69nc had me blowing off the idea at first. I am using the aaw harness. Right now I’m needing grounding mostly for dash/courtesy lights and the relay block. Don’t know if if the relays are electronic or mechanical. Maybe a dozen grounds. At this point the only electronic device is the classic auto air ecu. Probably add metermatch.and I guess a new radio. I probably could deal with those things separately. It would be easier. You think this could be harmless…….

[69NC 21]

I'm a former electrical engineer. I did embedded controller work for a major automotive tool manufacturer for about 10 years, then I switched to cloud services and enterprise architecture, pays better.

I still do it as a hobby.

[Vicfreg 771]

The relays are electro-mechanical.   As I recall, they have a ground wire just for those relays, and I found a local place to ground them to.   For my AAW harness, I took their under dash ground points, and grounded them to the metal structures under the dash.  The courtesy light grounds can be grounded locally also.  For your Classic Auto Air, look at the instructions.   My Vintage Air has a digital controller.  The instructions were clear to take 2 of their ground wires and run them directly to the battery.  This is to avoid electrical noise/interference with the fan motor that is part of their A/C package.

So, the short answer is for your AAW harness grounds, just use solid local ground points.  There are a lot of places under the dash to do that.  There is no reason to consolidate them.  For any electronics, consider a separate ground to the battery.

Good luck. I have lots of pics of my AAW install in my 1970 convertible if you need them,  let me know. I also have a spreadsheet I used to track every wire, function, and routing.