Boris113 Posted May 1, 2014 Share Posted May 1, 2014 Apologies in advance, but I've got a few questions to ask in one go The other day my alternator decided to throw it's bearings around the engine bay so I ordered a new Denso unit. I removed the goosed unit tonight and went to fit the new one but have come across several differences. On the old one, there were 3 wires connected to the back: 2 x thick brown wire and a smaller brown wire with a yellow tracer, along with the additional earth lead I fitted when the vehicle was having earthing problems. Unlike the old alternator which had no terminal markings, the new version has terminals labelled as B+, D+ and W. A look on Google suggests that both of the thick brown wires should go to the B+ terminal, and that the brown/yellow trace should go to D+ which is the charge light on the dash, could someone kindly confirm that is right? Assuming this is correct, then is the W terminal redundant unless a rev counter is fitted to the vehicle? Finally, the pulleys are different sizes, with the new unit being much smaller. As far as I am aware, the old alternator was a standard 65A whereas the new one is 100A, should I switch the pulleys over and use the larger one that matches the current auxiliary belt or retain the smaller version? Both alternators have the same width pulley in relation the the mounting points so the belt should run smoothly on either, but I'm not too sure if the smaller pulley will create slack in the belt, leading to it slipping rather than spinning the pulleys. Once again, apologies to ask lots of questions in one go but I wanted to check that I was doing the everything correctly the first time round. Harry Quote Link to comment Share on other sites More sharing options...
mmgemini Posted May 2, 2014 Share Posted May 2, 2014 Yes. Check that both the Brown wires go to the starter motor. Yes Swap the pulley Do you have a split charge system fitted ? Do not use the Brown/ Yellow for that. Quote Link to comment Share on other sites More sharing options...
Disco-Ron Posted May 2, 2014 Share Posted May 2, 2014 Can't help with the connections, but the old one is a defender unit, new one is disco, there are two belt lengths to cope with the pulley differences, you'd now be well advised to upgrade the wiring back to the battery to cope with the extra 35amps.... Quote Link to comment Share on other sites More sharing options...
Boris113 Posted May 2, 2014 Author Share Posted May 2, 2014 Perfect thanks guys I don't have a split charge, just 1 Numax battery and the original Tdi wiring so will connect the brown/yellow onto the D+ terminal. Having had a bit of a read around, people suggest adding a 16mm2 from the B+ to the starter motor, or better still direct to the positive terminal of the battery. I presume it's ok add this alongside the current wiring? Harry Quote Link to comment Share on other sites More sharing options...
mmgemini Posted May 2, 2014 Share Posted May 2, 2014 Harry Those two Brown wires fitted should go to the starter motor "live" connection. That's what I have and have had since I fitted the 100Amp alternator. Not had any problems. Have you got the heat shield cover for the back of the alternator ? If not I suggest you order and fit one. Quote Link to comment Share on other sites More sharing options...
cackshifter Posted May 2, 2014 Share Posted May 2, 2014 I 've just done this on 2 vehicles, there might be a wire from the W terminal to the EGR controls if you have those. 16mm2 is a good size, unless you are winching or something it will only carry anywhere near 100A for a short while, the most mine normally do is 55A with a heated screen and everything on. You can change the pulley but a better alternative is to fit the shorter belt (ERR5911 I think). If you are running a new wire, run the thick one and disconnect the original - if a poor connection develops you may end with more current than you wish going through the original. The original heatshield doesn't fit, and there is a school of opinion that says you don't need one. However I found that the back of both mine got quite warm compared to the front especially after a bout of towing, so have made heatshields out of a kind of laminated aluminium, a sheet is about £20 on ebay, with air intake at the bottom of the alternator, and mounted on stud extensions at the back of the alt, and they run much cooler. Quote Link to comment Share on other sites More sharing options...
mmgemini Posted May 2, 2014 Share Posted May 2, 2014 The heat shield on mine just swapped over. I was told by my electrician that the two wires were better than one ? ? Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted May 2, 2014 Share Posted May 2, 2014 The pulley size was apparently reduced to allow better charging at tick over, really can't remember where I read the that though. But it does make logical sense. Quote Link to comment Share on other sites More sharing options...
mmgemini Posted May 2, 2014 Share Posted May 2, 2014 The pulley size was apparently reduced to allow better charging at tick over, really can't remember where I read the that though. But it does make logical sense. Yes it does. I can't remember the size of the pulleys on mine but I haven't had any problems charging four batteries. Quote Link to comment Share on other sites More sharing options...
western Posted May 2, 2014 Share Posted May 2, 2014 This should help, it has been posted in this forum before Quote Link to comment Share on other sites More sharing options...
cackshifter Posted May 2, 2014 Share Posted May 2, 2014 Re the heatshield, if you get the pukka Disco alternator, then the ERR4859 heatshield would fit. I bought the 100A Denso alternators supposedly equivalent, to AMR4248 and AMR5425 labelled DENDAN008, but the rear is rather different, and the heatshield doesn't fit. http://www.woodauto.com/pdf/DEN2013.pdf. Quote Link to comment Share on other sites More sharing options...
Boris113 Posted May 6, 2014 Author Share Posted May 6, 2014 Thank you for all of the help chaps, I fitted the new alternator and all seems ok but the pulleys are slightly different. On the old one, the external fan and some washers act as a spacer whereas the smaller pulley on the new alternator has a spacer built in. I couldn't get the shorter belt over the bank holiday and needed the vehicle asap so in a rush to get it sorted, fitted the new alternator with the old (larger) pulley and it all seems ok. Stupidly I damaged the smaller pulley in the vice (not enough room for ring spanner + allen key) trying to remove it so replacement pulley and shorter belt are on order. I'll pinch a heat shield from a mate's scrap disco and all should be hunky dory once again. As a belt and braces approach, both of the large brown wires were running to the starter, but I put a 16mm2 wire back to the battery positive also. Harry Quote Link to comment Share on other sites More sharing options...
Ex Member Posted May 6, 2014 Share Posted May 6, 2014 D+ = Battery charge light, Brown, yellow trace. Large stud = 12V to battery Brown wires. W = Tachometer connection (not used) If this is a larger alternator (100 A versus 65 A) you should be really replacing the two brown wires with a single, larger capacity wire. 4 gauge is a good choice. Quote Link to comment Share on other sites More sharing options...
Mo Murphy Posted May 6, 2014 Share Posted May 6, 2014 Harry, put the Allen key in the vice, the ring spanner on the nut and then the end of the shaft onto the Allen key. Works for me HTH Mo Quote Link to comment Share on other sites More sharing options...
Boris113 Posted May 8, 2014 Author Share Posted May 8, 2014 Great stuff, thanks guys. I'm back off abroad shortly so the 90 is going to be laid up again but I'll sort the wiring out properly when I get back. Mo, I used your trick to get the old one off, but my ring spanner wouldn't fit inside the smaller pulley to get onto the nut and all I could do was clamp it on the vice in a last-minute attempt to get the vehicle useable again. Stupidly if I'd thought about it, I could have clamped it between some bits of timber so that it didn't damage the pulley I've had a look and some people say to crack the nut with a socket when it is still fitted to the vehicle, using the belt to hold it tight. Once the shorter belt and new pulley arrive, I'll see if it works and report back. Cheers again, Harry Quote Link to comment Share on other sites More sharing options...
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