Some of the SPF 40's have a factory wiring problem in the ammeter circuit that makes the meter read off scale. Not all cars have this problem which leads me to believe it's a QC issue. My car had this problem and I elected to replace the ammeter with a voltmeter as I believe that to be a better indicator of the charging circuit anyway (see the "How To" SPF GT Swap Voltmeter For Ammeter).
Below are two solutions to the problem. One is from Cantor (the harness manufacturer) and the other is from Dennis Olthoff. I personally prefer the Cantor version because I think it's a bit easier to do but both work fine.
Below are two solutions to the problem. One is from Cantor (the harness manufacturer) and the other is from Dennis Olthoff. I personally prefer the Cantor version because I think it's a bit easier to do but both work fine.