I'm replacing my battery for a smaller one and in the process I removed the short negative battery cable that is attached to the firewall.
Got pretty surprised to find the area behind the cable shoe painted, the only electrical contact seems to go through a few threads on that small M6 bolt.
Is this normal?
I'm tempted to brush the paint off, but on the other hand it seems to have worked ok so far so maybe I shouldn't bother.

 

Many of the grounds on this car are attached the same way, like you said it worked fine up to this point, it must be good enough.

 

You prolly already know this. I place a fine layer of grease (I use moly type) over the bolt and exposed terminal wiring after tightening the connection to ground. Helps to keep the contact corrosion free.

 

Yeah grease is good
Did some resistance measuring between the stock ground cable and the fuel rail and got around 7mΩ which seemed pretty good.
That stupid paint layer had to go though and with my new ground cable, slightly longer and a bit thicker I got 1.4mΩ.
Feels so much better now
Pics

 

I think most of the current flow is going to be through the bolt threads, not the paint layer under the bolt head.

Cable eyelet to bolt head, bolt threads to chassis. Lube the threads with a conductive grease (not a dielectric grease), to prevent corrosion and promote conductivity. Same lube between eyelet and bolt head and any washers.

 

You can always sand off the paint too to make a more direct contact. My 85 pickup had ground issues too, and that definitely helped.

 

Not sure if my previous post was unclear but the paint layer is sanded off now.
I'm using silicone dielectric grease, read this if you have doubts http://www.w8ji.com/dielectric_greas...ive_grease.htm

 

A clean ground is best but a little resistance won't hurt. The battery is only used to start the car anyway.

-- Chuck