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voltage spike

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amantinori

Contributing Member
while running the voltage hold at around 12v on my merc 5.7 with a 4 wire alt. this alt has a batt sensor wire, i havent seen this before so im not sure what it does exactly. my issue is the voltage will randomly spike to 14/16v then drop back down to 12v. as i tun on more and more accessories the voltage will drop to 10v. things liek the blower, radio, running lights. the motor doesnt seem to be draining the batt but if this is normal i dont want to go replacing the alt for no reason. can any one chim in ??
 
engine off
put the meter on the battery, record reading
start engine, @ 1000rpm 14V , alt is good,
if reading on dash is not the same , check for loose grounds.
 
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