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Strange Electrical Problem

paulrod

New member
"I recently was out on my Maxu

"I recently was out on my Maxum (454 Mercruiser)Bravo III and noticed that the voltage meter was low. I turned the Battery switch to off and the engine shut down which indicated that the alternator was out. Went back to dock and removed the alternator and found that the read lead was broken. I reattached and started the engine and was charging OK. Turned batteries off and engine ran OK. With Batteries off turned on electrical power (lights, pumps, etc.) and all was OK. When I hit the trim switch the engine shuts off instantly. Any Ideas?"
 
ohms law E=IR Volts = amps x

ohms law E=IR Volts = amps x resistance

The trim pump drew enough current to create a voltage drop great enough to kill ingition.

my guess
 
"You NEVER turn off the batt s

"You NEVER turn off the batt switch with the engine running,You risk a voltage spike that will fry eveything including the engine electronics!!!"
 
"Listen to the Doctur! Your Ba

"Listen to the Doctur! Your Batteries also provide stability to your boats electrical system. And, with todays "High Tech." systems our old ways just don't cut it. Your ECM, various sensors, Electronic Nav gear, Digital Components, etc. all rely on a very stable current flow. As Doc pointed out you risk causing a Voltage Spike because you have removed the main source of inline grounding for everything electrical on your boat. Now go stand in the corner until your sorry! Al W."
 
"definitly time to do a comput

"definitly time to do a computer check now that you did that and experienced those results,any other ODD occurances since?I would definitly worry about the ECM now.Just a thought."
 
"It's all irrelevant, sinc

"It's all irrelevant, since you don't run with the batteries off. What happens when you hit the trim switch with the batteries on? Kghost is right. The voltage draw may have dropped the voltage to a point where it will not fire the ignition system (9.6 volts)"
 
"Good points. When I hit the s

"Good points. When I hit the switch with the batteries on,the trim moves and the engine runs fine. I had no idea how much power the trim pump draws."
 
"One more thing,

Back when


"One more thing,

Back when the dinasors roamed the earth and we had mechanical voltage regulators between our altinators and batteries you used to be able to disconnect your battery from the charging circut to determine if you altenator crapped out. ( if the alt was good the motor would still run)

Now in the 21st century.............
When the voltage regulators went solid state and were incorperated into the altenators, when disconnecting the battery from the circut typically will fry the regulator and sometimes blow a diode ot two!!! THEY DO NOT LIKE (NO LOAD) VOLTAGE/AMPERAGE SPIKES........"
 
"I guess I'm just one of t

"I guess I'm just one of those old Dinosaurs. I remember those days when I used to work on my own cars...the '69 Charger R/T, the '70 Cuda. And then there was my '67 Chris Craft Cavalier. I used to turn off the batteries to see if the alternator was working. Enough reminiscing. Thanks"
 
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