1974 Scamp #2

With work and this heat (90* +) I haven't done much to the Scamp. I have been gathering parts to do a rear end swap to an 8.75. Ordered SS springs the other day and should be here soon. All I need is axles. Also pick up a kit to move springs in but thats going to be a winter project.
I've been scratching my head with an over charging problem. I have a volt gauge an a amp gauge in the car. At idle Im seeing 14 volts on the gauge and almost 40 on the amp gauge. RPMs go up so do the gauges. Battery is around 13.5 when running. Ive read and looked for and much info as I can. I'm not good at all with electrical problems. I've tired 3 regulators with no change. I've checked grounds. But today I ran a wire from the alternator to the positive side of the battery and bingo it works right. So what does that mean ?????