Re: My 620 will not turn off when I shut off the key? Why?

From: datsunaholic
Date: 11/28/02
Time: 11:18:51 PM
Remote Name: 208.186.7.117

Comments

Voltage regulator. My '74 did that when I got it- I switched out the regulator (not fun finding a '73-74 type, which uses a different plug than the later ones) and it quit doing that. The mechanical regulators seem to do that more often than the IC type (both types are available for 620s, and no I don't mean ones built-in to the alternator). But I've found the mechanical ones to last longer.

It's caused by a short in the field sensing circuit. With the ignition on the field gets power via the ignition feeding the coil via a relay in the regulator. When it shorts out the field input from the alternator continues to feed power to the ignition even with the key off (the field stays powered up as long as the alternator is spinning). Once you kill the engine the field drops, which shuts off the ignition and all seems normal.

One indication I had of this problem was the Charge light stayed lit all the time, even though the charging system was working. That may be a red herring diagnosis, though, as even after I replaced the regulator (which solved the engine won't die problem) the alternator light stayed lit. The charging system is working fine even with the glowing light- I now rely on a voltmeter to indicate charging status.