battery isolator 4.3 mercruiser

viper

Sorry if this is already out there; I was unable to successfully search for this answer.

I have a rinker 196 on a small lake.  I want to run my stereo without worry about the starting battery and to be able to start and stop the motor without affecting the stereo operation.  Many of you have this on your larger boat, I believe.

I bought a Noco 140 amp isolator.  My alternator is just 70 amps.  The motor is a mercruiser 4.3.

Looking at my instructions, I believe that I need to connect the 4th terminal for the excitation.  Also looking at the instructions I am led to believe that with my type of plug on the alternator I'm not able to use the isolator.  I believe I should be able to us the isolator.

Noco customer service has not been helpful but they agree that I should be able to hook it up and have it work, but they keep saying they will email me another supplement to the manual but it hasn't come through even after multiple calls.

Other research, the 4th terminal is used so the alternator puts out a higher voltage to compensation for the voltage drop from the isolator????

Other research states the 4th terminal is optional.

And lastly I have also seen that I should just jump the Alternator input on the isolator to the 4th terminal.  

212rowboat

I think you're over thinking it, my man.. but I don't blame you for wanting it right..

I run two batteries on a 4.3 too, but I just used a simple battery switch.. the amperage capacity doubled, the voltage remains the same.. I've got it easier because they are duplicate batteries.. I'm guessing you're using a bigger battery on one side?

You only want one lead only running to the alternator.. it should be clearly marked on the isolator.. bat1 hot lead to starter and engine harness, bat2 hot lead to accessory distribution block.. all negative leads to engine block, and isolator grounded..

You'll be adding a lead to the isolator from each battery hot line, and to separate points on the isolator.. you'll be rerouting the existing alternator hot to the alt in on the isolator.. the isolator is grounded.. that's four points on the isolator. the isolator doesn't care how much juice goes to it so long as it doesn't exceed the 140a..

viper

thanks!  I didn't think of the starter cable.  I'm still trying to figure out what cable is which.  Rinker wrapped the wires so neatly it is difficult to trace.  Thanks!