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Posted: Mon Mar 14, 2011 1:55pm

Post Subject: BMC 1500 glow plug problems

Hi Tony My bmc 1500 has been having problems with the glow plug circuit - I have fitted new plugs but that didnt do the trick. When I turn the switch to heat the plugs the solenoid just clicks rapidly - I have swopped this for a new one I am told that the wiring system is "heavily engineered" it had an old type push button solenoid which I have replaced with a newer equivalent - it still didnt fix the problem. I now suspect the other solenoid/relasy which is almost identical to the older type butr minus the push button - I am told this is a isolated return unit. do you think it could be this that is causing the problem? I am told a modern equivalent will cost about £80 but that I shouldnt need one.. I am getting rather confused - If I just turn the ignition to start the engine cold it will start after about 35 seconds, kick out a cloud of white/grey smoke for a few seconds which I suspect is unburnt diesel and then it runs fine. I think that if the glow plugs were to glow it would solve the problem, Have you any ideas please..Dave


Posted: Mon Mar 14, 2011 3:47pm

Post Subject: BMC 1500 glow plug problems

Without a wiring diagram it is hard to know exactly how your boat is wired but I think your boat has an old fashioned petrol car starter solenoid that does the power switching for the glow plugs. Although this is good practise few boats are so wired, most feed the glow plugs direct from the ignition switch. Unless your original solenoid was mounted on the actual engine or gearbox it would have had two thickish wires on the large nut type terminals which are the feed and supply to the glow plugs plus two thinner wires. One thinner wire ran from the ignition switch glow terminal to a 6mm push on blade on the solenoid. This is the energising wire. The other wire should be a negative (earth) connection which may have been on another blade on an insulated return solenoid or simply attached to a fixing screw so it earthed the body of the solenoid. It is possible that you have got hold of a solenoid that has one 6mm blade plus another one that may be smaller or the same size and you may have thought this is the negative terminal. It is actually used for ballast resistor ignition systems so you should ignore it. Now get the negative wire onto the solenoid case or mounting bracket then take a length of cable from the battery positive and touch it on all b;lade or small terminals (if its off a Ford it may be a small threaded rod). One should make the solenoid click and not click out until you remove the feed. That terminal is the one to feed from the ignition switch so put the relevant wire on and see if it clicks as it should. If it machine guns (what I think you are describing) see below. I can not work out how you can get that machine gunning unless you have a bad battery negative connection somewhere between the engine and battery. If your master switch is in the negative it would be my first suspect - especially if it has a plastic key. However such a fault would make it impossible to start so I wonder if the ignition switch has gone resistive, but again I do not see how that would energise the starter solenoid but not the glow plug one. I think you need to carry out voltdrop tests on all the relevant circuits but it is hard to describe them on here so please email me so I can send you some more info. Tony Brooks PS for inland use you can get away with an earth return solenoid if you wire it as I describe or you could change it for a 40 amp relay.

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