Try a hobby store, they should have good quality plugs that will handle 30-40 amps continuous for R/C car batteries. Make sure you get the good quality kind for racing, they are usually made out of silver or gold. I've been out of the R/C stuff for a while so I can't remember the who makes them but if you go to a good hobby store they should be able to find what you are looking for.
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Gary T.
2001 Silver Ice
4x4 SE Auto