Hi all. During the process of getting my engine fired up a few weeks ago, I had to use a booster pack to get enough voltage to the coil thus thinking a new battery would be the order of the day.
However just tinkering with the electrics Ive noticed the iginition circuit goes through a relay. This creates a drop in voltage when the key is turned to its first position and therefore instead of getting the 12.6 volts at the coil Im only getting 11.2 volts. Im not sure why this has been done but I know the boat has been converted from 6v to 12v in the past and the instruments are all original 6v running on the 12v. I did buy a 12-6v reducer for the fuel gauge but didn't end up using it as it made no difference.
So my question is, is it normal for the ignition to go through a relay and create a voltage drop in the process? I have tried by-passing in order to get the 12.6 to the coil and the engine fires up much better, but the gauges don't work. Before I go any further with it, is there a valid reason why it may have been set up like this when it was re-wired?
It probably has a ballast resistor in the circuit (or did have). In this system the coil will be a 9v coil & it is fed through the ballast resistor which drops the voltage from 12v to 9v for normal running. However when you are cranking the engine the ballast is bypassed sending 12v to the coil giving a much fatter spark to aid start up. As soon as the engine starts & the key is released then the coil operates at 9v. I suspect that is the what the relay is doing - bypassing the ballast resistor. Often coils are mistakenly changed for 12v ones which mean they are running under voltage. Alternately people bypass the ballast resistor & run the 9v coil at 12v permanently. Ether one means trouble!
Mercs are like women, no 2 are exactly alike. That's what testing is about. In general it is safer to test motors and props than women!
Thanks. Maybe I should have said that I replaced the coil with a more powerful matched one for the electronic points I fitted.
Anyway, just had another look on the relay and I found when I disconnected the the auxillary connection to the relay (No 87, the one that provides the power to the instruments etc. when ignition on), I found that I get the full 12.6 volts through the relay and also at the coil. As soon as a re-connect the voltage drops to 11.2.
For information, my permanent live comes in though the ammeter and then onto the ignition switch before going up onto terminal 30 of the relay.
It appears to be an issue with the instruments causing the drop in voltage, but do you think it would be safe to take the instrument feed direct from an ignition live rather than through the relay, or maybe even through another relay? Like I said earlier, none of the instruments are fitted with a 12v-6v reducer so Im thinking this may have something to do with it, but that's just a guess.
This is the reply from the supplier of the electronic ignition / coil
'The coil is designed to run at 12-14 volt. It must not run at 9V. If the coil gets 9 volt the ballast resistor or the ballast wire has to be removed (or a new wire made to the coil)'
So Im guessing I bypass my gauges for the minute. Should I still wire my gauges through a relay?
The only ignition live Ive found is that coming off the relay, so Im stuck with that one. Anyway, just spent another hour tinkering again and I found that the voltage drop was happening after the ignition live was connected to the temperature gauge. Messed about with all the live feeds off of the same terminal and I found if I disconnected the one marked Ampmeter on the loom, I got the full 12.3v again. Thinking this was linked to the alternator, I then removed the smaller lead from the back of the alternator and hey presto I got the full 12.3v at the coil and at the instruments etc.
Now my question is, I have a gadget with a curly wire between the alternator and the coil as shown in the photo. Is this the ballast resistor I need to remove and have a direct wire back to the coil?
