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Mercruiser 350 CIDElectrical problem

H

hippie

Regular Contributor
"When running my engine last w

"When running my engine last weekend the gauge which shows how much the engine is charging the batteries was at a solid 13 volts. Now this weekend when I started the engine it only climbs to "just beneath" 12 volts. How do I check to find out which is bad, the voltage regulator or the gauge? Thank you, Bob"
 
"Separate volt meter is usuall

"Separate volt meter is usually the easiest. Depending upon which alternator you have, you may have to raise the RPM to ~ 1500 to get it to start charging.

If you suspect the alternator, any good electrical shop (or auto parts store) should be able to check it. If it needs work, use a shop that knows what "marine" means."
 
you need a shunt and a volt me

you need a shunt and a volt meter

or

an amp clamp

then you need to put a load test on the battery
 
"First, make sure your battery

"First, make sure your battery terminals are very clean and tightly connected. Rev up engine a bit and test what voltage is going to the batteries - it should be 13 - 14 volts. If not, check voltage coming directly off alternator -regulator. If too low, you have a bad alternator or regulator. If that voltage is okay, then, pull the gauge, disconnect the + terminal and connect a good voltmeter to test the voltage coming into the gauge and see if is the same voltage as on the gauge. If not, gauge is faulty. If they read the same, then you have a wiring problem between the battery and the volt meter."
 
"Well, I just spent two full d

"Well, I just spent two full days on this problem.} We tested by a voltmeter on the alternator which is outputting 14.9 volts. The men at the dock said to check the alternator by starting the engine and then pulling both positive leads from the batteries. We did that and the engine runs fine without the batteries. Then this morning I went to start the engine and while cranking the engine it backfired numerous times. My tachometer and speedometer also started going around in the opposite direction that they normally turn. Once the engine is started the gauges work fine and the engine runs fine. Also, the one battery was discharged this morning, which indicates a short to me. What is the matter and how do I fix it? My mechanic is off for two weeks so I must fix it myself. Thanking everyone in advance. Bob"
 
"NEVER disconnect the battery

"NEVER disconnect the battery leads on a running engine. Removing the battery causes transients (voltage spikes) that can cause havoc to gauges, ignition systems, radios.........some have protection diodes and some don't - maybe you just got lucky.

Did you check for something left ON, powered by the battery that died? If not, you can use an amp meter to see what the current draw is. Then you just get to isolate your circuits until you find the 'problem'."
 
"Makomark, Nothing was left on

"Makomark, Nothing was left on and the battery would crank but then stopped but yet there was no "clicking" like comes from a dead battery. The backfiring only is when the motor is being cranked over. The gauges went haywire a day after the leads were pulled off, after a lot of starting and testing went on. My guess is a short somewhere (maybe in the starter or how about the bilge pump wired direct to that battery). Wherever it is it has to be shorting continous to keep the volts down at 11 on the meter. What do you men think? Thank you, Bob"
 
The starter may be the culprit

The starter may be the culprit drawing to many amps causing the guages to dance when starting etc it would be whats causing all the problems
 
Another problem I have found i

Another problem I have found is in the connectors on the cables going to the engine. Mine look like trailor plugs with about 10 connectors. When the srop making good contact they can cause problems in the guages.

Clean them and put a dielectric grease on them before plugging them back together.
 
"I got mad and pulled the alte

"I got mad and pulled the alternator off and had it tested at a shop. The man said the problem is a loose wire as evidenced by the positive stud out the rear of the alternator being "welded". We put another stud on and now I'm charging at 14 volts. Thanks to all who helped, Bob"
 
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