There are a number of post from a guy named nachort74 here on the board - he's the guru in my eyes about that...

So the "trick" would be a stronger alternator that can load the battery in idle.

First I would recommend to attach a voltmeter to check voltage at the battery when idling and at about 2000rpm.

(The trick "with the cable" is to fix melted bulkhead connectors at firewall or even ampere-meters - but if you check your battery you will find out if any bad connecitons are your problem)