Often when I turn the key on my 34 Street Rod, the whole electrical system goes dead (SBC). I replaced the battery - no change. If I remove and clean the terminals, I get 3 or 4 starts, and then dead. I then tap the positive terminal connection, and it starts. The battery is in its own compartment behind the seat. Its not a heat sink problem since it happens even when cold. The build is about 12 years old and this problem started about 2 years ago. Any thoughts?
Animal

Check all your connections from the battery and to the starter, especially the grounds. Does your accessory power run from the battery or the big terminal of the starter? Check those too.

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Thanks. I'll check.

The battery cables (positive and ground) need to run from the battery direct to the starter. Many times the frame is used as a ground and it will work OK at first but later the connections degrade.

Also, you could have a bad battery cable (where the lug is crimped on) even though it looks OK.

vicrod

Doc here,

You could also have a cracked battery terminal..Does the terminal (s) seem to be "Moist" when you clean them? That's a sign it may be cracked and the post internally melted..Load test the battery to eliminate that.

If your running a remote solenoid, check the connections there also, for a test, Bypass the remote Solenoid by bolting the cables together and temporally insulate (or bolt both cables to one side, along with the fuse buss cable) around the joint, then try it .. If it runs good replace the solenoid. The contacts may be burned or pitted.

Inspect the Starter solenoid for melted (wobbling) terminals in the plastic housing, and loose terminals..this can cause intermittent conditions also.

Doc

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More good places to look. Thanks all