Need help--C3 interior grounds

[Hib Halverson]

I'm working on "Yellow Thunder" my old 71 hot rod and the ex-Vette Magazine "BBfH" project car. I had it up for sale but after three months and no serious offers, in spite of a price reduction, I've decided to take it off the market for a while and do some more work to it.

One project is to replace the Edelbrock air/fuel ratio meter and narrow-band oxygen sensor I've had in the car for 15 years or so with a more modern and more accurate Auto-Meter AFR gauge which uses a wide-band O2S. This process forced me to deal with a long-standing high ground resistance problem the car has. Many of the aftermarket electrical accessories in the interior are grounded to the "birdcage" at a grounding point behind the passenger side dashboard trim. The problem is between that point and the negative post on the battery I read 8-8.5 ohms resistance, which is too high.

The service manual only notes the existence of "instrument panel cluster" and "console "cluster grounds" not the locations of those. My guess is both of them are located behind the dashboard trim somewhere on the metal of the birdcage structure. Does anyone know the locations of those grounds to a higher level of accuracy than I find in the FSM?

Also, is the birdcage grounded to the chassis through its mounting bolts or are there grounding wires or straps and if there are wires/straps, does anyone know where I'd find them?

Lastly, if anyone here has experienced the same problem, ie: high resistance in the ground circuit between body grounding points and the negative battery post, please post your experiences.

 

[Vettehead Mikey]

Hib,

On '73s there is most definitely a braided grounding strap that goes from the passenger side #1 body mount down to the frame. Not sure on earlier solid body mounts but would imagine that it's similar.

Don't remember specifically where along the birdcage the instruments etc. ground is attached, it's been 12 years since I needed to get under there.

 

[Hib Halverson]

Thanks "Vettehead Mikey". I had the vent grille off on the driver side and didn't see a strap, but I'll get the passenger side off and look there.

 

[shark454]

I believe there is a ground point on the metal birdcage structure behind the dash and slightly to the right of the radio (a bit higher than the radio horizontilly). I have a 72 and when the dash was out, I remember seeing a ground connected to that horixontal metal frame. For my original Stereo as an option option FM radio, there is an additional amplifier located behind the dash there and it grounds there.

HTH

 

[Hib Halverson]

I never did find any stock ground straps. Don't know if they were removed at some time in the past or just rotted/rusted away.

So, I added a new one from the birdcage metal above the #1 body mount down to the frame. That, a new 10ga ground wire from a grounding point behind the dash back to the battery and new negative battery cable solved all my problems.

 

[6880 Mike]

Tacho and speedo each have a separate ground; console trim plate should have a spade lug on the underside for the console ground, probably in front of the ash tray door. Not sure the center cluster has a separate ground, but I ran a separate ground to my clock and it's run like a charm ever since.

Main dash harness grounds on the driver's door post.

 

[Vettehead Mikey]

I never did find any stock ground straps. Don't know if they were removed at some time in the past or just rotted/rusted away.

So, I added a new one from the birdcage metal above the #1 body mount down to the frame. That, a new 10ga ground wire from a grounding point behind the dash back to the battery and new negative battery cable solved all my problems.

Glad it worked!