On Jun 12, 12:20*am, Steve B. wrote:
I'm 99.9% certain it's a broken earth strap. You can usually check easily with a
heavy duty jump lead placed between some good (unpainted) contacts points on the
engine block and car chassis, re-making the connection, unless it's further back
the chain right at the battery (but unlikely).

Graham

When you hook up the battery backwards (the OP did) it doesn't cause
the "earth strap" to break. *It burns out the fusible links or blows
fuses and maybe even cooks some electronic components.



Alternator diodes are a good possibility. And many other more
expensive things
if they were not polarity protected.

* * * * *Steve B.