Got a horsebox that dosent charge,changed alternator,now I only get 14.5v at back of alternator when my isolator is in the isolate position,I get this readingbetween battery + and chassis earth isolator side aswell,but not to batterys because of being isolated.The rest of the time I only get 12.91v to the batterys. Have cured previous battery drain from tacho and lack of charge because battery light was disconnected.any help appreciated. Thanks in advance

joe, April 2013

Could I just confirm that the 0813 is a 12v system and not 24v ?

Jason, June 2014

Check battery voltage with engine off (doesn't matter what position isolator is in if you check at battery terminals). Should be getting 12 to 13 V say. Start engine with battery on. Should now be getting about 14.2 V at battery terminals, if not then alternator is u/s. If tachometer is operating then alternator must be OK as alternator supplies pulses to operate tachometer.

JD, April 2013