BCM Community

Heres an interesting electrical story. I was helping a friend diagnose his 4106 starter. It quit suddenly one day and he had pulled it out figuring on getting it rebuilt. So Im messing around with some jumper cables checking it out by putting power directly to the motor side of the solenoid and case. Nothing but a tiny spark. I keep messing around while were talking and suddenly a big spark and it spins a bit. Move the jumper clamps around a bit more, nothing. More messing around and this time I discover if the jumper clamp is touching the actual threaded motor stud it spins. Turns out an insulating film had formed between the motor stud and strap even though tight. Just though Id pass this on.

-Tom P.

Tom,

Thanks, this type of stuff is good to know.

I've found that battery posts do the same thing after a year or two, they turn black which is insulation. I just finished cleaning mine off, try to do it every 18 - 24 months.

Most connections, especially the large cables, do the same thing but it isn't black.

Gus, you may have noticed that the hard black surface only forms on the positive post. I've had good luck avoiding this by assembling cables to posts after applying petroleum jelly.

For what it's worth.

Tom Caffrey