volts are 13.8 at idle and down to about 13.4 which wipers lights and stereo on

 

Can you purchase a rebuild kit for the auto switch located on the gear box that selects the gears, 600 to 800 seems a lot for a new one. I have pulled old one apart and cleaned, two tabs were burned out which I cleaned, was working fine for a while but know playing up again won’t select reverse or drive but will select 123 any recommendations on weather you cans replace the contact points tabs slides or do I have to purchase a new one

 

There are a number of threads about this issue on the forum -- and most of them are far more recent than this one (the last post here was nine years ago).
But a quick summary is that the XYZ needs to be adjusted correctly for it to work. If you loosen the mounting bolts you will be able to rotate it slightly to get it into a position where all the gears register properly.