Help finding ballast resistance in the coil wiring

[lawson]

Hi guys i hope u can help me out...i bought a boat with a 3.0l mercuser its about 1989-1988 with points system..to cut a long story short i got sold a boat that needed a lot of work doing to it...ie wrong gearing in sterndive for a 3.0l which i have got the mechanic to replace with the 1.98.1 gearing and lots of other things that also needed doing...i bought my boat for ?3900 and have already spent over ?2000 haveing work done on it getting it ready for summer...however the mechanic said ok we are ready for a sea trail this saturday and we took it out..its a 19 foot fletcher cuddy sports cruser....it ran great and with 3 guys onboared we where doing over 36mph and i was so happy but then things started to go wrong...it started to misfire bad..maybe on three then two then died on us...he opened up the engine bay and said oh the timing cover is leaking oil must be gasket or both rotted timing cover which will need replaceng...but thats not the misfireing reson...he said he thinks its the coil...so after the boat had cooled it started again fine and we ran it to the quay side where a friend of the mechanic met us with a new coil..so he replace the old coil with this but said we should not go out again today as timing cover is leaking oil and it needs to be replace be for we can go out underload again to make sure it was the coil caurseing the misfire...however and this is where i need some help...i have read on this forum and other forums that my age of boat has a ballast resistance in the coil wiring and will need a coil designed for external resistance...i told this to the mechanic this morning and he said thats not true all mercs are 12v system and said the it does not need a coil designed for external resistance...so can someone please tell me where to find this ballast resistance in the coil wiring so i can show him...or if he is indeed correct please tell me .... i dont know what would happen if he put the wrong coil on but i would like it to have the correct coil for my boat and feel a bit happier at sea without this going wrong in the summer....thx for anyhelp

 

[Bondo]

Re: Help finding ballast resistance in the coil wiring

so can someone please tell me where to find this ballast resistance in the coil wiring so i can show him...

Ayuh,... It's the wire itself,.... Put a multimeter on it,+ Check the voltage,...
Resistored, it'll be in the 9V area,... Unresistored, it'll be 12Vs...

 

[lawson]

Re: Help finding ballast resistance in the coil wiring

Thx Bond-o i will do that ...and i think u are also sure that my boat has a coil designed for external resistance...so what i think u must mean is to put a test meter over the new coil with the key turned to the run position and look for 9v as opposed to 12v...and that way i can show that indeed it has ballast resistance in the wireing and ask him to fit the correct one...could anyone tell me what would happen if the wrong coil was fitted?....just out of intrest..thx

 

[pole position]

Re: Help finding ballast resistance in the coil wiring

Some coils are made with the resister built in. It should be printed on the outside of the coil.

 

[Bondo]

Re: Help finding ballast resistance in the coil wiring

so what i think u must mean is to put a test meter over the new coil with the key turned to the run position and look for 9v as opposed to 12v

Ayuh,... Disconnect the wire from the coil 1st, then test for voltage, with the key On...

 

[lawson]

Re: Help finding ballast resistance in the coil wiring

Some coils are made with the resister built in. It should be printed on the outside of the coil.

yes i am sure u are correct...however i am not a mechanic i am just trying to make sure he fits correct coil and how to tell if he has...so if he put a coil on with a resister built in and i had a resister in the wiring to it would this still be ok...is that what u are saying...or would it drop the voltage even futher by have a resister in the coil plus one in the wireing?....thx

 

[lawson]

Re: Help finding ballast resistance in the coil wiring

Ayuh,... Disconnect the wire from the coil 1st, then test for voltage, with the key On...

Thx bond-o i was getting a bit confused with this....but i understand what u are saying and after reading on the net about resistance and coils i understand more now...basically to find out if my boat has resistance in the coil wiring just drop a meter on the coil + wire with key in run position with good ground from engine to meter - lead and that will tell me weather it has resistance in the coil wiring....if it reads 12v then i dont need a coil designed for external resistance...if 9v i do...can anyone tell me if indeed the mercursers with the points system was infact built in the first place with the external resistance in the wireing....cos when i test the voltage if it is reading 12v then the resistor in the coil wire has been removed....and the system has been modified...

 

[wire2]

Re: Help finding ballast resistance in the coil wiring

Ayuh,... Disconnect the wire from the coil 1st, then test for voltage, with the key On...

That will read the full battery voltage, with or without a resistance in series. The only load is the voltmeter (A digital Fluke is 11 MegOhms input) so there's virtually no current, hence no voltage drop across the resistor. Ohm's Law.

The + wire needs to be on the coil, and the points must be closed for the coil to draw current, and show either a full 12v or ~9volts. To close the points, disconnect the hi voltage lead from the coil tower so the engine doesn't start, then bump the starter. With a few bumps, the meter will show either 12 volts every time, (no resistor) or randomly alternate between 12 and 9, (with a resistor).

OR, take the distributor cap off, turn the crank ,if needed, with a wrench to close the points, and read the voltmeter.

 

[wire2]

Re: Help finding ballast resistance in the coil wiring

yes i am sure u are correct...however i am not a mechanic i am just trying to make sure he fits correct coil and how to tell if he has...so if he put a coil on with a resister built in and i had a resister in the wiring to it would this still be ok...is that what u are saying...or would it drop the voltage even futher by have a resister in the coil plus one in the wireing?....thx

You should not have a resistive wire AND a coil with a built in resistor. The 2 resistances will be in series and drop the voltage to the primary coil windings to 6 volts. That means a very weak spark at the plugs

Experiment with a voltmeter to determine if the wire is resistive as I've described above. The coil will state on it if it has a resistor.