Ditch lights relay box bolt size for inside hood?

I’m in process of putting on some ditch lights. Though I need to ground the relay. It’s the existing one on the side panel. What size bolt I use for this? Thanks

 

I usually do the grab bag approach and test-fit extra bolts till one works lol. Or if there is bolt near by that is convenient/safe to remove, it might fit (threads are likely to match) Then I take it to the hardware store for a match.

That’s just me though, because Im so easily distracted that if I need to look on the internet, my day could easily be shot by the time I get on track.

Once you put in a bolt, tighten it down and check for zero ohms across to the negative batt terminal. Sometimes paint in the thread gets in the way of a good ground.

 

Or just use the mounting bolt of the relay box. I just checked it and it grounds O ohms with a little scratching of the coating.

 

Tried that. The small relay box hole is too small for that bolt.

 

You want metric threads. This is what I used.
Hex cap screw, M8-1.25x20.
I’ve also used a smaller screw in other places:
M6-1.00x16.

 

Ah, I totally misunderstood. I thought you were looking for a place to put a ground wire.