[cardoc]

Bad grounds cause this. The system can only pull from what is available. What's worked for me is adding a 4ga cable from the battery to the firewall. It increases ground conductivity and helps with power flow. The cable is available at most parts store and you can get it with eyelets on both ends to make it easy.

 

[cardoc]

By "what's worked for me" do you mean it fixed the dimming issue 100%? Or did it improve it markedly?

It corrected a lot of issues. My VDC came from Boston. A lot is rust at ground lugs, undercarriage bolts, etc.. One of the first things I did was clean up every ground in the engine compartment. The conductivity measured excellent only losing 50 amps between the battery and block and 75 between the battery and firewall. Dimming went away. I added in the 4 ga and it improved to a 40 amp loss to the body. This also helped a great deal when I overhauled the sound system.

Any time you reduce electrical flow loss, its an improvement. Corrosion is an inhibitor. Silicates are inhibitors. Loose connections. But you also have to have a good source and that is the battery.

Upon installing the SC, I added more grounding to handle the loads I created with added sensors, gauges and the 2 cooler pumps. I also now use a deep cell battery.

 

[cardoc]

I add grounding to a lot of cars. All makes/models when the need comes up. What you should try is a cable from the battery to the block. Or, bolted right up to the alternator bracket. Or, you could go to the bolt at the bottom of the AC. Still leave the one you put on the chassis.

Have you cleaned the grounds on the firewall?