Grounding a battery horn.

[Reno Speedster]

I am getting ready to install a one wire battery horn on my 22. It’s the one that mounts with a head bolt and a water outlet bolt. The parts are painted so I need to get a good ground through the bracket to the bolt/block. I was thinking of just using a split washer and letting it scrape the paint on the bracket. Alternatively, I could use one of the multipoint lock washers and let that dig in or scrape a bare spot under the head of one or more of the bolts. What have other folks done that works?

[TRDxB2]

I am getting ready to install a one wire battery horn on my 22. It’s the one that mounts with a head bolt and a water outlet bolt. The parts are painted so I need to get a good ground through the bracket to the bolt/block. I was thinking of just using a split washer and letting it scrape the paint on the bracket. Alternatively, I could use one of the multipoint lock washers and let that dig in or scrape a bare spot under the head of one or more of the bolts. What have other folks done that works?

I would not put anything "extra" under a head bolt - best to keep as many threads as possible. Also that might cause some misalignment with the water outlet bolt. The water outlet bolt is likely to make a better ground since its threaded into the block with cleaner threads (note the gasket is a possible insulator). So looks like just a lock washer between the water outlet head bolt & bracket. Also you'll need to insure that the bolts from the bracket to the horn provide a good ground as well.
Note the differences
--Split lock washers are helical-shaped split rings. When fastened, the two ends exert a spring force on the fastener to create increased friction and resistance to motion. Helical spring lock washers are the most common form of a lock washer and are best suited to applications with smaller loads.
--Internal tooth lock washers have teeth made to bite into the nut/screw head and surface it contacts. They work best on small screws or screws used in electrical grounding.
--External tooth lock washers (also called star washers) have teeth made to bite into the bearing surface. An external tooth lock washer is designed to provide stronger holds than internal-tooth washers as the teeth bite into a larger radius and are best suited to large screws.

[Steve Jelf]

A toothed (star) washer should do. It has multiple contacts.

[Scott_Conger]

I'd highly suggest that the washer have these two attributes:

made from phosphor bronze
have an external tooth pattern

https://www.mcmaster.com/bronze-washers ... washers-9/

From Columbia Metals: Phosphor bronzes are a major group of engineering alloys noted for their strength and toughness coupled with high corrosion resistance. Phosphor bronze alloys are used extensively for electrical and electronic components, connectors, marine hardware, fasteners, valve spindles, pump and drive shafts, bearing bushes, gears, instrumentation components and many other critical applications where the particular blend of mechanical properties, spring properties, oxidation and corrosion resistance, low magnetic permeability and wear resistance can be used to full advantage.

Heck, it might even make a good lock washer!

Seriously, electrolysis/corrosion between dissimilar metals can potentially effect nearly every combination of metals, including Stainless steel of every alloy, but in reality and real world, if electrolysis as a problem with phosphor bronze that would be news to the owner or operator of every ship, boat or submersible with a prop.

[Craig Leach]

I prefer good clean flat surfaces of all the same material. Dissimilar metals can promote electrolysis. Star or toothed washers are good for
cutting through paint and rust that should have been removed for a good connection. The NFPA national Fire Protection Association prohibits
there use on fire, rescue and emergency vehicles because they will collect moisture between the contact & noncontact surfaces causing
corrosion. Most of these washers are designed as a locking device not a electrical connection enhancer. a good split lock washer will do the
same and give better contact. The ground is the second half of the circuit and as important as the hot side. when in doubt go back to the
battery. I always put a ground cable from a pan bolt to the frame rail the ground is on. If you have ever seen sparks fly out of the front
motor mount when the starter is cranking you will too.
Craig.

[TXGOAT2]

Engine grounding is important. I've seen a metallic temperature gauge capillary tube and oil gauge pipe glow red hot when the starter was engaged. A poor engine ground allowed heavy starter current to flow through the metal gauge connections to ground at the hole in the firewall.

[Humblej]

Just clean the contact areas of the head, block, and horn bracket.