1998 Bravo 7.4 Alternator Exciter Wire Not Showing 12V....

[San_Diego_SeaRay]

.... at the end that connects to the alternator stud. I can physically trace it back to to a wiring harness branch that wraps around the back of the engine near the distributor, probably terminating near the cannon plug. Without tearing apart the harness (aka electrical tape), any ideas where this thing gets its 12V from? A wiring diagram doesn't help when everything is wrapped up like it is. For the record the Alt Merc Part number is 817119A4.

Thx.

EDIT: I should state, it basically shows 0.00v on the voltmeter.

 

[alldodge]

The ALT has 2 wires (not counting the black ground)
Red/Purple which comes from the 50 amp breaker (constant power)
Purple which comes from the ignition switch (switched power)

 

[San_Diego_SeaRay]

The ALT has 2 wires (not counting the black ground)
Red/Purple which comes from the 50 amp breaker (constant power)
Purple which comes from the ignition switch (switched power)

Yeah. It's the purple wire (maybe purple/yellow if I recall?). Isn't that the exciter wire? Shouldn't it have voltage in the RUN position? I'm not getting 14v+ when the engine is running. Alternator isn't getting hot. I should clarify: I'm looking for 12V when the purple wire is disconnected. I put one voltmeter lead to the end of the purple wire and the other vm lead to a known good ground while the engine is running. Shows 0 volts.

EDIT: OK I see what you might be getting at. Should I test for continuity at the canon plug? Should one of the engine side terminals have min resistance to the end of that purple wire at the alternator?

 

[alldodge]

Yes, it should have power when key is ON
Same supply as to the coil

Is this a MPI or carb, serial numbers are best

 

[San_Diego_SeaRay]

Yes, it should have power when key is ON
Same supply as to the coil

Is this a MPI or carb, serial numbers are best

Serial Number 0K281139. This is the carb'd model. Not a MAG MPI.

 

[alldodge]

Thanks
There is most likely a break in the splice. Can run a jumper from the + side of the coil to the ALT

Power is going thru the cannon plug

 

[San_Diego_SeaRay]

Thanks
There is most likely a break in the splice. Can run a jumper from the + side of the coil to the ALT

Power is going thru the cannon plug

OK thanks for the help. I think you've got me going in the right direction.

I did previously jump 12 volts to the exciter stud on the alternator and then it did start putting out 14+ volts. So I know it's the circuit, not the alternator. But I didn't know how the purple wire was routed. Now it all makes sense; being tied into the coil wire and being fed from the ignition. I'm gonna pull that canon plug apart and start testing. Strangely, my coil recently had a spell where it was only getting ~10 volts. Now it seems to be fine. But there might be something going on inside that leg of the harness. Hopefully I'll be able to find something.