jonnyswamp Posted October 15, 2020 Share Posted October 15, 2020 Hi mate, yes I remember this from the other site..... A wiring diagram would come in real handy around now..... Can you get a voltage reading from the wire that connects to the battery terminal on the alternator and a voltage reading across the battery? Hi, we were getting the same reading of 15v on both, or do you mean just testing the alt cable when not connected to batteryThese pics are one of the new ones and the originalThe alternator feed to the batteries went through a heat sink first, then on to the split charge unitIt made no difference when the heat sink and charge unit were bypassed, nor when a direct earth was run from the block to the batterySent from my SM-G981B using Tapatalk Attachments: Quote Link to comment Share on other sites More sharing options...
jonnyswamp Posted October 15, 2020 Author Share Posted October 15, 2020 Have had the 3rd new alt tested and it's good When power is removed from the red wire terminal (under test) it starts upping the voltage to 15.4, fine when connected So sounds like you were on the button with your diagnosis suzook That red wire going to the reg/rec, does it com from the back of the ignition switch ? All the alternators came with 2 flying leads, red and purple, which connect to the wiring harness via bullet connectors The fault/break will be between the connector and the ignition switch? Quote Link to comment Share on other sites More sharing options...
jonnyswamp Posted October 15, 2020 Author Share Posted October 15, 2020 Just in case anyone is confused, I copied and pasted part of the original post from the other site rather than type the whole thing again Quote Link to comment Share on other sites More sharing options...
suzook12 Posted October 15, 2020 Share Posted October 15, 2020 Hi mate, effectively it can come from the switch, although could be relay fed etc, that's where the wiring diagram comes in. What would also be an easy fix would be to replace the flying leads, much chinese stuff uses very poor wire, so making a couple of leads out of proper automotive grade cable wouldn't go amiss. To find the other end without a schematic, you will need to be belling out (long length of test lead, disconnect and connect to test lead and "bell" for continuity with multimeter). Once found, disconnect and test with a "megger", this will give you an idea of how good your wire is... Alternatively, run a replacement wire and see if it cures it.... Hope that makes sense? Quote Link to comment Share on other sites More sharing options...
suzook12 Posted October 15, 2020 Share Posted October 15, 2020 Also, if it is fed from the switch, see what voltage you are getting from the switch, a worn contact inside the switch that drops the voltage output is quite common. You could either replace the switch should this be the case, or install a relay to feed direct from the battery and use the now redundant wire to activate the relay Quote Link to comment Share on other sites More sharing options...
jonnyswamp Posted October 15, 2020 Author Share Posted October 15, 2020 Will be going down tomorrow to refit and do the tests you mentioned 👍 Andy135 1 Quote Link to comment Share on other sites More sharing options...
suzook12 Posted October 15, 2020 Share Posted October 15, 2020 👍 Quote Link to comment Share on other sites More sharing options...
jonnyswamp Posted October 16, 2020 Author Share Posted October 16, 2020 (edited) Getting confused now Traced the red flying led from rear of alt (it connects to a green harness wire via a bullet con) this goes into a wiring centre and is made off with heat shrink Hasn't been connected to anything since I have owned the boat Run a temp cable from battery to red flying lead on alt and voltage drops from 15.4 to 14.5 The other flying lead on alt gets battery voltage via a relay once engine is started Help Edited October 16, 2020 by jonnyswamp incorrect info Quote Link to comment Share on other sites More sharing options...
jonnyswamp Posted October 16, 2020 Author Share Posted October 16, 2020 Quote Link to comment Share on other sites More sharing options...
suzook12 Posted October 16, 2020 Share Posted October 16, 2020 I would connect the red to back of the switch then, I have a feeling the relay is the charge light relay, so with engine not running it supplies pos feed to the alt, soon as alt is running polarity reverses putting light out..... Not sure why someone would disconnect the red/green wire, it's obviously supposed to be connected as bourne out by your testing What engine/ alt is is? Will see if I can find a wiring diagram Quote Link to comment Share on other sites More sharing options...
jonnyswamp Posted October 16, 2020 Author Share Posted October 16, 2020 That purple wire was giving the alternator battery voltage via a relay when engine was started The red wire on the right is a temp one from the battery When wired like this the battery voltage was 14.5v I removed the temp red cable, put the purple one in its place and the voltage is still 14.5 Is this OK Quote Link to comment Share on other sites More sharing options...
jonnyswamp Posted October 16, 2020 Author Share Posted October 16, 2020 The only info I have was a sicker on the original alternator (mando)which said Replacing LPA01926 This was cross matched to the one that's on there now The engine is a 230hp mercruiser (black engine) on a 2004 boat Do both of those flying leads need to connect to something, obviously the right hand one (red/green) hasn't been for some time Thanks for your patience zook Quote Link to comment Share on other sites More sharing options...
jonnyswamp Posted October 16, 2020 Author Share Posted October 16, 2020 Just zoomed in on the back of the original alt and the left hand wire (purple/pink) goes on the terminal marked exc, with the red/green on the one marked S So S was never connected to anything, or are the connections opposite in the alt I have now Quote Link to comment Share on other sites More sharing options...
suzook12 Posted October 16, 2020 Share Posted October 16, 2020 exc will be exciter. this is the one that should be connected to your charge light, it goes pos frrd to alt light to alt, with the alt providing the neg, soon as engine is fired, then the alt outputs pos so the light is effectively getting =12V from either side and goes out.... The S terminal is your battery voltage sensing wire.... So what has basically happened is your alternator has been running flat out and died. Luckily for you 15V seems to be its cutoff overall or you'd have a lot of dead electronics.... Quote Link to comment Share on other sites More sharing options...
jonnyswamp Posted October 16, 2020 Author Share Posted October 16, 2020 Something not adding up here then, nothing is connected to the exc terminal (battery light still goes out when started) The cable that was connected, I put on the S terminal and all seems fine with an output of 14.5 v when running I appreciate your time on this, but it isn't making sense I'm away tomorrow, but will go down Sunday morning and take a pic of the back of it, with terminal letters visible and maybe you can tell me what should go where and how/why it appears to be working now Quote Link to comment Share on other sites More sharing options...
jonnyswamp Posted October 16, 2020 Author Share Posted October 16, 2020 www.ebay.com/itm/NEW-ALTERNATOR-FITS-MANDO-65-AMP-MERCURY-MARINE-VOLVO-PENTA-807653T-AC165610-/323263426603 This identical to the new one currently fitted (and the one that failed originally) Quote Link to comment Share on other sites More sharing options...
jonnyswamp Posted October 16, 2020 Author Share Posted October 16, 2020 https://www.ebay.co.uk/itm/Alternator-Mercury-Marine-OMC-12-14-VOLT-65-AMP-ARCO/312673862892?hash=item48ccd084ec:g:oD0AAOSwUR9cxfkx Don't think the first link worked Quote Link to comment Share on other sites More sharing options...
suzook12 Posted October 16, 2020 Share Posted October 16, 2020 Common practice is to link the B terminal to the S terminal, which would explain why the red/green wire was not connected. The downside of this is it reads the voltage at the wrong end..... The exc ia def connected to switchable power source, alternator lights can be a bit less simple these days So if you link out B to S your dilemma will be solved, If you want a more accurate charge voltage, connect to the battery isolator switch, boat side. I guess the two terminals are connected to some extent internall and probably provides enough to power the exciter coil Quote Link to comment Share on other sites More sharing options...
jonnyswamp Posted October 17, 2020 Author Share Posted October 17, 2020 I'm doubting what I think I know I've done now I'm going to boat tomorrow morning and will take a pic/video of it all Thanks Quote Link to comment Share on other sites More sharing options...
jonnyswamp Posted October 18, 2020 Author Share Posted October 18, 2020 Did what you said and all seems good U da man Cheers zook Andy135, suzook12 and Saintly Fish 2 1 Quote Link to comment Share on other sites More sharing options...
Andy135 Posted October 18, 2020 Share Posted October 18, 2020 8 hours ago, jonnyswamp said: Did what you said and all seems good U da man Cheers zook Well done Swampy and well done Zook 👍 Is this our first fix of the new forum site then? jonnyswamp 1 Quote Link to comment Share on other sites More sharing options...
JonC Posted October 18, 2020 Share Posted October 18, 2020 13 minutes ago, Andy135 said: Well done Swampy and well done Zook 👍 Is this our first fix of the new forum site then? No, I diagnosed Fistys turbo issue for him. But we’ll done zook for sussing this one out. Quote Link to comment Share on other sites More sharing options...
jonnyswamp Posted October 18, 2020 Author Share Posted October 18, 2020 I've posted on my thread that I started on ws f, to say that Suzook sorted my problems after I bumped into him on another boating forum It may pique someones interest Andy135 1 Quote Link to comment Share on other sites More sharing options...
JonC Posted October 18, 2020 Share Posted October 18, 2020 I took the liberty of attaching a link, not been booted off yet. Andy135 1 Quote Link to comment Share on other sites More sharing options...
Andy135 Posted October 18, 2020 Share Posted October 18, 2020 Well done Swampy and Jon. The more awareness of the site the better 👍 Quote Link to comment Share on other sites More sharing options...
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