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Posted: Tue May 04, 2010 10:58pm

Post Subject: No aux charge glow plugs not working

I changed my glow plugs on a BMC 1500 diesel about two weeks ago.The engine started fine every time on trial starting.Last Thursday we tried to start and after half a minute of cotinuous cranking and lots of blue smoke the engine fired.We then cruised for 6 hours and found that although the aux battery ammeter showed a charge the battery had lost some of its power.So we changed to aux battery 2, and after another days 5to6 hours crusing the second battery had not been getting a charge although the ammeter showed it had. The engine battery is charging fine. With the ignition switched on the oil and ign lights are on ok.So i checked for glow plug volts on the glowplugs, there was none.There was12 volts on the ign switch, but nothing to the glow plug relay.I have removed and checked the relay and is ok.Could it be a faulty split diode charge relay, ignition switch or earth(negative) fault? It was strange that both faults appeared at the same time. Any suggestions as to the next step of investigation? Thankyou, John.


Posted: Wed May 05, 2010 9:14am

Post Subject: No aux charge glow plugs not working

Dear John, there is so much you have not told me about this. You seem to have two "aux" batteries that you changed over. How did you change them - physically or by a big switch. If physically how are both charged or are they actually wired in parallel. If it's a big switch then you seem to have three banks. One engine battery, charged via a split charge diode and then two "aux" banks charged by the other output of the diode. This is very unusual and what leads to my next comment suggests to me that you might not understand your system. First of all any glow plug relay should have TWO lives on it. One is normally permanently live and usually fed via a fuse that could be anywhere along that cable plus a live that only becomes live when the ignition switch is in the GLOW - not aux - position. The glow position could be one click anticlockwise from off or two clicks clockwise from off. In the latter case the switch should have two "sprung" positions after "on" the first being glow and the second starts but the plugs will still be fed if you go straight to start. The next thing about the question is that you do not quantify the charge on the "aux" ammeter so I have no way of knowing how much and what the reading did over time. You see if you really did have just 12 volts on the ignition switch then you have very flat batteries, it should be at least 12.2 to 12.3 and from a diagnostic point of view the exact value is important. I also need to know it the alternator is battery or machine sensed. This is because if you really do have a split charge diode system a machine sensed alternator will normally never fully recharge a battery. Your question about what to do now is very hard to answer because I have been given grounds to doubt your level of electrical knowledge so perhaps the first two steps would be to go onto my website ( and printout the relevant sections of the electrical course notes so you can work through the glowplug circuits and charging circuits. Then, as this may be a long job, email me directly ( a better description of your systems and symptoms with any volatge readings to one decimal place. I suspect that once you have looked at the glowplug with relay circuit you will be able to do a better test on it and possibly sort it out. I also think that as you have been working in the engine bay you should have a very good look around for lose and broken wires/terminals. I honestly can not comment about the charging until I get some ammeter and volatge values and also some idea about how many ammeters you have and what they are supposed to be showing. I am sorry I can not be much more help at this stage and I do appreciate how difficult it is to know what to put into these questions and what is not needed. Tony Brooks

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