Voltage Drop

[Rstorrie]

Bought a used 1987 boat with a mercruiser 230 GM 5.0L V-8 that has the Thunderbolt IV ignition System. Traced down some ignition parts that were faulty and got it running. Question I have, if any of you know about the Thunderbolt ignition systems, is I get between 12.2 and 12.5 volts everywhere from the battery to the coil on all the + connections, but I get around 11.9v at the ignition amplifier with key on at + terminal on the coil with the amplifier connected to the coil. When I remove the amplifier wire from the coil, it goes back up to over 12v. Is this normal for Thunderbolt system?

(New cap, rotor, ignition sensor, key switch, kill switch, all connections on the boat either replaced or cleaned to bare metal)

 

[Scott Danforth]

Bought a used 1987 boat with a mercruiser 230 GM 5.0L V-8 that has the Thunderbolt IV ignition System. Traced down some ignition parts that were faulty and got it running. Question I have, if any of you know about the Thunderbolt ignition systems, is I get between 12.2 and 12.5 volts everywhere from the battery to the coil on all the + connections, but I get around 11.9v at the ignition amplifier with key on at + terminal on the coil with the amplifier connected to the coil. When I remove the amplifier wire from the coil, it goes back up to over 12v. Is this normal for Thunderbolt system?

(New cap, rotor, ignition sensor, key switch, kill switch, all connections on the boat either replaced or cleaned to bare metal)

you should not have more than 0.1 volt drop from the battery to the ignition switch and back to the coil

my guess is one of the cable connections between the motor and the helm will have corrosion.

 

[Rstorrie]

I do, the little drop only happens with the ignition amplifier is connected, then goes back up when disconnected. Amplifier drawing current?

 

[Rstorrie]

Just to make sure I probed all the wiring from the battery, to the key switch, to the kill switch to the starter solenoid, to the front of the engine harness plug, to the other side of the engine harness plug, and the coil, all 12.5v

 

[Scott Danforth]

you still have corrosion. hook up a test light (load) and you will probably see the same amount of voltage drop.

the 0.1 volt drop should be what you see with a 1 amp load, not the 0.00000001 amp load of your meter. at 5 amps you would see about .18 volt drop (assuming 16 gauge wiring and 20 feet of run)

never prob thru the wiring insulation