Okay, let's analyze the options for repairing your Toyota starter anode contact, keeping in mind the environment (high current, frequent switching, arcing) and your desire for a durable, cost-effective solution. Given the inherent challenges, none of these options are guaranteed to be as reliable as a new component, but we can aim for the best compromise

Assessment of Your Options
a. surface weld on copper to eroded area - high risk of damage to bolt



Pros

Copper welding (TIG or MIG) can provide a good electrical connection and build up the eroded area.

Cons



High risk of damaging the bolt

The heat involved in welding can distort the bolt threads, weaken the metal, and even melt nearby components. It's VERY difficult to control the heat precisely enough to avoid these issues. The arc resistance of the copper will be good, but the surrounding metal may be softened.

Verdict



Generally Not Recommended. The risk of damaging the bolt outweighs the potential benefits. It requires specialized skills and equipment. b. just silphos filler on the eroded part



Pros

Lower temperature than welding, easier to apply with basic torch setup. Sil-phos will provide some arc resistance but is relatively brittle.

Cons



Not durable enough. Sil-phos (silver-bearing brazing alloy) is better than solder, but it's still not designed for high-current, repeated arcing applications. It's not as mechanically strong as copper welding, and it's more prone to cracking under vibration and thermal stress. The silver content is relatively low, so the arc resistance will not be superior. Verdict



Weakest option. It might work temporarily, but expect it to fail relatively quickly. c. I have coin and 99% silver pieces, silphos15 silver contact area to existing bolt



Pros

Higher silver content could improve arc resistance and electrical conductivity. Coins are often not pure silver, so I would suggest using only the 99% silver. The use of sil-phos 15 is the same as using silver solder. Sil-phos 15 also has a low mechanical strength.

Cons



Still has inherent risks. It depends on the coin alloy and the filler rod's composition, and if any of the coins are corroded, you should not use them. Joining silver to the bolt is not as strong mechanically as a single piece. If the silver detaches it may cause a short. Verdict



Potentially Better than B, but still limited. The higher silver content might help, but the mechanical strength and risk of failure remain concerns. d. straight brass braze rod. filler Pros

Brass is more robust than solder, good conductivity

Cons

Brass is an alloy of copper and zinc. It has inferior arc resistance and conductivity compared to pure copper or high-silver alloys. Brass braze filler has fairly low melting temperature and poor mechanical strength.

Verdict



Similar to B, potentially better if your only concern is conductivity. Not a great choice for arc resistance.

Recommended Approach (Compromise for Durability & Feasibility)

Before anything, clean the existing bolt thoroughly with a wire brush or abrasive pad to remove all corrosion, grease, and loose material. Good surface prep is critical for any of these to have a chance.1. Option C modified with caveats

If you are determined to use the coin/silver + sil-phos route:

Use ONLY the 99% silver. Avoid the coins if they aren't pure silver and/or corroded. Minimize Heat

Apply heat gradually and locally, just enough to melt the sil-phos and bond the silver. Avoid overheating the bolt. Use heat sink paste if you have it.

Build a Robust Shape

Try to create a slightly domed shape with the silver to provide a good contact point. Use a small file to smooth it after the silver cools.

Testing

Before reinstalling, thoroughly inspect the joint for cracks or porosity. Use a multimeter to verify good electrical conductivity.2.

Consider a Partial Solution (If all else fails)

Clean the existing bolt contact area as best as possible. Apply a thin layer of

conductive grease (NOT regular grease) to the contact surfaces. This can help improve electrical conductivity and reduce arcing, even with a slightly eroded contact. You can find conductive grease at auto parts stores or electronics suppliers. This is a band-aid, not a permanent fix, but it might buy you some time.

Important Considerations Safety

Wear appropriate eye protection and gloves when working with a torch or grinder. Work in a well-ventilated area.

Heat Management

The biggest risk is damaging the bolt with excessive heat. Use a small torch tip, apply heat gradually, and let the bolt cool down between passes. A heat sink compound or wet rag placed on the opposite side of the bolt head can help draw away heat.

Reassemble Carefully

When reassembling the starter, ensure all connections are clean and tight. Loose connections will contribute to arcing and premature failure.

Final Recommendation

While a new starter is the best option, if you're set on repairing it, a carefully executed modification of option C, using only the 99% silver and minimizing heat input, gives you the best (albeit still limited) chance of success. Remember that any repair is a compromise, and the longevity of the repair is uncertain.Good luck! Let me know if you have any more questions. Flag for review