Alternator overcharging? what does this wire do?

[BradleyPLKD]

Thanks in advance for your help! I have a 1996 Volvo Penta 5.7L carbureted gas motor (GL PLKD). I was having issues with my ignition modules going bad so started checking for bad ground and/or alternator overcharging. Grounds were all good but the alternator was charging 15.5V at the battery at 1300 rpm so I replaced it. However, the new alternator is charging at the exact same rate. So now I am wondering what could cause this? On my diagram, I have hooked up 4 wires (orange power to B, black ground to E, tach purple white to P, and ignition purple to EXC. There is also a jumper wire that links EXC to S (shown in red in my diagram). Is this jumper wire correct? What does it do? Might there be some other cause for the overcharging? Thanks!

 

[bruceb58]

Looks fine. Not sure why your tach wire isn't hooked up to your distributor but that is a separate issue.

Also, measure the voltage at the sense/excite line. If that voltage is low, the alternator will try to compensate by raising the voltage.

As another test, disconnect the jumper between the excite and the sense and run a wire from the sense to the battery itself and see what your voltage is.

 

[bruceb58]

On the AC tap, that wire should be going to your electric choke...not your tach. Hope you don't have it feed back to your ignition as well.

 

[BradleyPLKD]

Hi Bruceb58. Thanks for your reply. Sorry, my mistake, the wire to AC tap is going to my electric choke (not tach). In the diagram from my original post, it says the purple ignition wire should go to EXC. However in this other diagram I found for a similar engine (LK year, GL model though different displacement) the purple ignition wire goes to the S terminal (not EXC). Could this be the cause of my problem?

 

[bruceb58]

Since you have a jumper between the exc and the S, it doesn't matter.

 

[BradleyPLKD]

Hi bruceb. My voltage at the both sense and excite is 13.5. Voltage at B at 1200 rpm is 15.4. When I remove the sense side of the jumper so nothing is connected to sense, voltage at B is still 15.4. I will try and run a direct line from battery to sense next to see if voltage changes. thx!

 

[BradleyPLKD]

Hi Bruceb. Okay ran a direct line from battery to sense. Still same voltage at B of 15.4. Thanks for your help...

 

[Lou C]

Interesting. I was having a similar issue with my '88 OMC. The alt is original and looks just like the one in your diagram. I bought a new ARCO alt. In the instructions it said that may OMC installations may have problems with over charging because the sense wire gets its voltage reading from the wire that comes from the ignition circuit. Over time resistance builds up and gives a lower voltage reading. This is what leads to over charging. If you are reading correctly and your sense terminal on the Alt is getting true battery voltage and you still have an over charging issue, then maybe the regulator is faulty. Since you have a Volvo that was made during the joint venture period between OMC and Volvo, the alt wiring may well be the same as OMC's.....

In the instructions ARCO said to run a jumper from the S to the B+ terminal on the alt and tape up the sense wire in the harness....