Mercruiser 4.3L electrical wiring diagram

[lou23]

I have a 2000 Princecraft Vacanza with a 4.3L Mercruiser and it has a melted ground wire in the dash from the tach to the fuel gauge. There is an amp draw that drains the battery and disconnecting the harness to the dash gauges stops the draw. I’m looking for a wiring diagram to try and trace the short. It’s a 4.3L Alpha/Bravo 262 cid Gen+ S/N OM346613, Model 4211025PS. Any help appreciated. Thanks

 

[Chris1956]

look for melted wires in the wiring harness.

I would expect a wiring diagram to be avail, maybe at maxrules, but not sure that will help a lot.

The gauges are daisey-chained together for ground and lighting and power.

 

[lou23]

Can I assume the melted wires would be in the harness running upstream towards the gauges as the amp draw stops when I disconnect the coupler? It would be easier to disassemble the harness under the dash than to try and follow the harness downstream back toward the engine and battery. Thanks

 

[alldodge]

The Red/Purple wire comes from the motor thru the ignition switch and then to the gauges. If disconnecting the gauges stops the drain then then I would see if the key switch is the issue, or something has been connected to the wire. Could also be that the wire coming from the motor

 

[lou23]

alldodge, looks like part of your post about the wire coming from the motor got cut off. I’m assuming the Red/Purple wire coming from the engine should always have power and feeds the ignition switch. With the key off there should be no power going to the Purple wire which powers the gauges and also feeds the alternator when in the Run position and powers the Yellow/Red when in the Start position. If I disconnect the Red/Purple at the ignition switch and my amp draw disappears I would assume I have a bad ignition switch. Thanks

 

[alldodge]

Your correct and the red/purple comes from the motor 50amp breaker (7 top pick) and goes to the key switch thru pin 6 of the engine 10 pin connector

 

[lou23]

Thank you very much. I may not have a chance to work on this until next week but I will let you know.

 

[lou23]

Everything checks out good. I started and ran boat up to operating temp and thought it was fixed. Shut it down and checked battery voltage which was at 12.12 volts. Checked it less than 2 hours later and it was at 5.6 volts. Checked the amp draw which was at only 0.07 amps. Could this be a bad battery? I’m at a loss.

 

[alldodge]

Could this be a bad battery?

Yes

 

[Chris1956]

The test is to charge the battery and disconnect it. Now check it 2 hours later and see what it is.

A .07A load is nothing for a good battery, but you need to prove the battery is bad, IMO.

 

[achris]

I bought one of those battery testers. Cost 60 sheepshagistan dollars. Works so well... Worth every micro-peso.

Ancel BA101...

Chris.....

 

[lou23]

This started with finding a melted ground wire (burned through and separated) from the main ground off tach to the fuel gauge. Also found a bad pin and slightly melted ground wire at dash harness heading to gauges. Repaired both and also installed a battery switch to disconnect power or add 2nd battery. All the gauges now work (fuel gauge was not working before) and the amp drain with all off is about 0.07 amps. Battery fully charged gets to about 12.5 volts but will not hold the charge. Drains to about 3 volts overnight and will lose like 6 volts just sitting for a couple of hours. The battery is about 6 years old so I think a replacement would be a good idea. Hopefully replace it this weekend and I will report afterwards. Really appreciate all the help and advice on this forum. Thanks.

 

[lou23]

Installed new battery and took boat out for a couple of hours. Ran great, all gauges worked, no issues. Parked overnight and battery was down to about 7 volts by morning. I have been checking the amp draw off of the 2 two smaller gauge connections on the battery. One is a combination Black/Green and the other is maybe a 8-10 gauge single black. If I combine them and run them through the meter I show about 0.7 amps maximum draw. Should I be pulling the main ground cable as well and run all 3 through the meter? I figured the main ground was only for starting and wouldn’t have any drain when just sitting, key off. Thanks

 

[lou23]

Sorry, meant to say 0.07 amps, not 0.7.

 

[alldodge]

Try disconnecting the alternator and see if the leakage stops

 

[lou23]

Do I just unplug the connector with Red/Blue stripe and purple wire or do I need to also disconnect the Orange wire and the Ground? Thanks

 

[alldodge]

I would disconnect all and if it stops then try reconnect. That said if it stops then the ALT has the issue

 

[lou23]

Disconnected all wires to the alternator, charged the battery full and left it in the lift. Won’t be able to get back to it until next week some time. Hopefully it’s still charged. I’ll let you know. Thanks again.

 

[lou23]

alldodge- I just got back to my boat today. Voltage when I left 4 days ago was 12.86 and today it’s at 12.56. Great call on the alternator! I’m assuming the diodes failed. I would have never thought to suspect that. Thanks
Now I have to either purchase a new/rebuilt one or see if I can find someone that rebuilds them.