Low voltage on merc 4 strokes
08-30-2020, 09:02 AM
#1
Registered
Thread Starter
Join Date: Feb 2012
Location: Sarasota FL. Priest River ID
Posts: 1,131
Received 1,285 Likes
on
474 Posts
Low voltage on merc 4 strokes
2017 Merc 150 4 strokes, low voltage alarms came on both engines yesterday.
Batteries are new and voltage is low regardless of battery switch settings. (12.2)
Any ideas? My knowledge of all things electrical sucks.
I have the longest warranty available but not sure if electrical is covered for the entire warranty.
Just weird that both had issues the same day.
Could running the battery switch set for both cause the alt/reg’s to mess with each other?
Batteries are new and voltage is low regardless of battery switch settings. (12.2)
Any ideas? My knowledge of all things electrical sucks.
I have the longest warranty available but not sure if electrical is covered for the entire warranty.
Just weird that both had issues the same day.
Could running the battery switch set for both cause the alt/reg’s to mess with each other?
08-30-2020, 11:18 AM
#2
Registered
My super duper very limited understanding on the Merc four strokes is that Merc wants them to have their own dedicated battery mine are 2017 200 HP verados starboard battery is dedicated and the switch is either on or off (no 1,2, both)same for port battery switch it has only on/off the house battery has 1,2 and both and an ACR in the system on the house battery.
Just because Merc wants something a particular way doesn't mean that boat mfg. always do it that way it may be worth figuring out which battery goes to what engine isolate the batts that way and see what you have.
I am for sure interested in what the problem is on yours and best of luck
Just because Merc wants something a particular way doesn't mean that boat mfg. always do it that way it may be worth figuring out which battery goes to what engine isolate the batts that way and see what you have.
I am for sure interested in what the problem is on yours and best of luck
Last edited by Awash; 08-30-2020 at 11:21 AM.
09-04-2020, 08:56 PM
#3
Registered
Remove engine cowl. With engine running put your Voltmeter on the alternator output. Check if it is giving 14.4 volts.
if yes, then check it directly on the battery. Is it getting the 14.4 V ? If yes, then issue could be with guages.
If no, go back to engine, there is big red wire on starter, place voltmeter on it and check voltage. If 14.4 then charging system is working fine.
If alternator gives 14.4 but battery and starter wire showing 12 or less, then most probably the inline fuse is blown.
Follow wire from alternator, it goes behind / through black electric box. you need to take out the bolts for the box to have some loose.
The big red wire going from alternator to starter that runs through the black box has a 100 Amp inline fuse on it. Remove the wire from both ends and test fuse.
If blown, that is your problem. Mercury dealer sells replacement wire/fuse harness for about $75. You can buy the fuse online or at auto parts store for about $5
Can build your own replacement wire / fuse harness for about $10 and 30 minutes of your time or buy the merc for $75
Either way, once you solve that issue you now have to find out what caused to to blow in the first place.
Check electric system for shorts, bilge switches, float switch, electrical panel etc
My boat has twin 150 Fourstroke. We have a battery bank for each engine. 2 batteries each with switch 1,2,or both. motors start and work fine in any configuration of switches
if yes, then check it directly on the battery. Is it getting the 14.4 V ? If yes, then issue could be with guages.
If no, go back to engine, there is big red wire on starter, place voltmeter on it and check voltage. If 14.4 then charging system is working fine.
If alternator gives 14.4 but battery and starter wire showing 12 or less, then most probably the inline fuse is blown.
Follow wire from alternator, it goes behind / through black electric box. you need to take out the bolts for the box to have some loose.
The big red wire going from alternator to starter that runs through the black box has a 100 Amp inline fuse on it. Remove the wire from both ends and test fuse.
If blown, that is your problem. Mercury dealer sells replacement wire/fuse harness for about $75. You can buy the fuse online or at auto parts store for about $5
Can build your own replacement wire / fuse harness for about $10 and 30 minutes of your time or buy the merc for $75
Either way, once you solve that issue you now have to find out what caused to to blow in the first place.
Check electric system for shorts, bilge switches, float switch, electrical panel etc
My boat has twin 150 Fourstroke. We have a battery bank for each engine. 2 batteries each with switch 1,2,or both. motors start and work fine in any configuration of switches
