antno Posted August 17, 2014 Share Posted August 17, 2014 Hello My car is a 96 tt6 jspec I've got a problem with my charging system. I thought it was just an alternator so I have ordered a new one from mr t. The alternators not due in till end of sept so I bought a second hand one to get me about until then. The second hand one turned out to be one off an auto so it was a bit bigger and the connectors were in a slightly different place. I got her fitted but when it started I heard some electrical arching. Stripped it down and it looked like it was getting hot around the rectifier. Some of the paint had melted. So I stripped my original one down and again I found the rectifier burnt out I had been driving with this till the dash lights lit up. I checked the terminals that connect to the alternator and the main battery feed (b) was live. The white wire to the regulator was live (12.5v). The yellow wire was to ground. And the yellow and green wasn't connected to earth or live. This was all with the ignition switched off. Also the alternator body was earthed and had a resistance of 3.4 ohms. With ignition on all three reg wires became live. The White was 12.5v the others were 12.0v My questions are. Should that yellow wire be grounded when the ignition is off? Also had anyone else had rectifiers burn out? Cheers antno Quote Link to comment Share on other sites More sharing options...
antno Posted August 17, 2014 Author Share Posted August 17, 2014 The yellow wire goes to the ignition switch according to the Wiring diagram Quote Link to comment Share on other sites More sharing options...
absz Posted August 17, 2014 Share Posted August 17, 2014 should have a resistance of below 0.5 ohm between alternator body and battery negative, check the earth connection between chassis and engine. Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted August 17, 2014 Share Posted August 17, 2014 The diodes in that rectifier are dead as a dodo. Quote Link to comment Share on other sites More sharing options...
antno Posted August 18, 2014 Author Share Posted August 18, 2014 Sorry I double checked the alternator body to earth this morning and it is 0.4 ohm but when the ignition is switched on it goes up to 7.6ohms. Is this normal? This was all on a cold engine with no wires connected to the alternator. Do you think a bad earth could fry the rectifie? Quote Link to comment Share on other sites More sharing options...
antno Posted August 18, 2014 Author Share Posted August 18, 2014 Anyone know if it's normal for the resistance on an earth the go up from .4 to 7.6 ohms when the ignition is switched on? Quote Link to comment Share on other sites More sharing options...
absz Posted August 18, 2014 Share Posted August 18, 2014 No it should not go up. if you have some jump leads connect the negative lead to the battery NEG and the other end to the engine block somewhere and recheck resistance that will confirm if you have a bad earth. poor connections increase load so its possible to burn diodes Quote Link to comment Share on other sites More sharing options...
SR86 Posted August 19, 2014 Share Posted August 19, 2014 I agree it should go up... Have you grounding double checked it could be a loose or off. Quote Link to comment Share on other sites More sharing options...
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