Need HELP!

Rstorrie

Seaman Apprentice
Joined
Jul 14, 2019
Messages
41
I bought a 1987 Chaparral 20' boat with the Mercruiser 230, V8, 5.0L Thunderbolt IV ignition system. I am at my wits end chasing a starting issue. Put on a new carburetor, ignition coil, cap, rotor, and spark plug wires. Sometimes it starts, sometimes it doesn't. Been checking the voltage at the + positive side of the coil and get around 8v with key on. (No start), Other times when I turn the key on, I get almost 12v (11.5v) and the boat will start. All the wires are connected and cleaned. What is causing the constant change in voltage to the coil and the no start? I cannot figure out why the voltage drops?
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
70,465
Ayuh,..... Welcome Aboard,..... Probably corroded wirin' connections,......

Start at the battery, 'n clean to shiny metal, Clean, all of the wirin' connections,.....

Pay attention to the Grounds, 'n both ends of the wires,.....
 

Rstorrie

Seaman Apprentice
Joined
Jul 14, 2019
Messages
41
Cleaned all the battery connections and all the connections on the engine, so should be solid. Get 12v readings at the ignition switch and kill Switch. I do have a new ignition switch arriving today as the old one is pretty ugly, but I cannot understand how an ignition switch would only put out smaller voltage when turned on, if that is the issue?
 

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
40,581
Corrosion of any kind is a resistance, and resistance lowers voltages. This can happen on and in wires, and on and in connections like a key switch
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Don't forget the 20A fuse under the dash (feeds the key switch). It can get corrosion on the ends and become resistive.

Chris....
 

Rstorrie

Seaman Apprentice
Joined
Jul 14, 2019
Messages
41
Yes, new ignition switch arrived and I put it in with new connectors. Now getting 12v on both sides of the coil and fires up every time. Never knew a ignition switch could do that. Thanks for the help.
 
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