Help - how to wire from Prestolite to 3-wire Delco alternator?

[camparks]

I have searched and searched, but I can't find it addressed anywhere what is to be done with the other two wires when replacing a Prestolite/Motorola with a 3-wire alternator. Does anyone know how to address the wires removed from the 'A.C.' and 'IND' terminals off a Prestolite/Motorla 4-wire alternator?

I have the wiring diagram and attempted to trace them. The Purple w/White wire from the A.C. terminal goes to the electronic choke - no problem there I will just work in a relay somewhere to switch it with the ignition. The Green wire appears to go to the Fuel Pump - here it gets tricky. I am pretty sure that the pump did not run until the engine cranked or was running(alternator spinning) since it was attached to the alternator on a diode - also a reason why OMC put a anti-siphon fuel barb on the tank preventing backflow to keep fuel right up at the pump. As far as I can remember, I never heard the pump run when the key was turned to 'on'. I assume this is to keep the carb from flooding?

Could someone verify this for me? If this is the case, what would a suggestion be to replicate this condition(no power to the pump unless cranking/running)? The old alternator completely bit the dust, so I don't have it to test and to verify that there was no voltage to the pump until the alternator started spinning during cranking and running. It has been replaced with a Delco 10SI 3-wire.

 

[Don S]

Re: Help - how to wire from Prestolite to 3-wire Delco alternator?

 

[camparks]

Re: Help - how to wire from Prestolite to 3-wire Delco alternator?

Again, it has not been addressed on how to re-wire the wires that were formerly on the LIGHT and AC diode contacts off the old Prestolite/Motorola alternator. The above diagram only addresses how to wire the EX and S leads - Excite and Sense. Fuel pump and Choke leads have nothing to do with those connections as they are draw current, not supply.

Is there any more information or clarification I can provide for help on this?

 

[Don S]

Re: Help - how to wire from Prestolite to 3-wire Delco alternator?

You can't wire everything to work with that alternator, it doesn't have the options.
You need the AC tap for the choke, and the L terminal is needed to operate the fuel pump relay. Get the correct type of alternator if you want everything to work.

 

[camparks]

Re: Help - how to wire from Prestolite to 3-wire Delco alternator?

I am not trying to get the wires to work with the alternator, as they can't - I can't make diodes appear on an alternator that doesn't have them. I am trying to figure out how to properly re-wire the fuel-pump lead. Instead of offering criticism, it would be more beneficial if you would read an entire post and atleast try to understand what is being asked prior to responding and actually offer a real resolution.

I know that the Delco swap is very popular. There are dozens of posts about changing from the Prestolite or Mondo to the Delco, but they only ever address the re-wire of the Excite and Sense. I am sure that someone out there has done this swap and properly re-wired the Choke and Fuel Pump leads, or other such per given model year.

For now, I will just do the logical fix which is place a relay behind the alternator. I will feed the switch with a lead off the wire for the Excite/Sense(switched by ignition key) with power coming off the B+ terminal so they get priority voltage. Hopefully someone constructive will come along and offer a second opinion on this to let me know if I did it correctly or not.

 

[krclose3]

Re: Help - how to wire from Prestolite to 3-wire Delco alternator?

I am having the same problem i have a 89 23ft phaser with a 351w in it. I have switched to a electronic distributor,mallory coil,performance plugs and wires. When replacing all that i took the alt off and had it tested it was bad like everything else. The local alt shop sold me a 1 wire said it was easier less wires just snip the old wires and tape them up. well that is not the case one of those wires is running to my coil, one is to the elec choke and i dont even no what the other one goes to yet. I need help with these wires and were to put them. The boat will crank but the key doesnt turn it off i had to pull the wire off the coil to get it to stop. ANY IDEAS.

 

[camparks]

Re: Help - how to wire from Prestolite to 3-wire Delco alternator?

Look through the diagram I have attached. I took this from a 1986-1998 OMC Manaul, just like I did the diagram for mine above. The choke wire should be Purple w/White. As for the others, you will have to do some testing with a volt/multimeter to confirm which wires are hot or switched with the ignition. If you don't have one, see if you can find a spare light and socket around you can use - if it lights up, you got power through there.

The Purple and Red w/Purple appear to be the old Excite lead and Sense leads. What I cannot tell is if they are all connected or not. The Red w/Purple appears to be the one that would switched with the ignition. If they are spliced together, both will be switched as they share the same current feed. If that is true and you wired them to the alternator output, that would be why your engine won't shut down when you turn the key off. What you need to do is introduce a relay like I did. You will need to test these two leads first though. It is possible that they are separate so you will need to wire them differently to the relay.

With the wires disconnected from everything, test for voltage with the key off and again with it on. If both show power with the key on, then use them as a feed for a relay to power the Choke lead. If only the Red w/Purple shows power, then you will use it as a feed for a relay to power the Choke and the Purple wire(which appears to power the coil). Use a standard Bosch type relay. You can find them with either a mounting eye or a harness that can be mounted. This is a standard type of relay used in automotive and marine applications in power distribution blocks for fans, fuel pumps, ABS systems, etc. You will only need to use 4 terminals on it: 86-Switched power from the ignition key, 85-Ground wire ran to any ground location(close-by bolt or such), 30-Positive power from alternator output, 87-Power going out to the Choke(and coil if determined from testing). 87a you won't need to use.

 

[bruceb58]

Re: Help - how to wire from Prestolite to 3-wire Delco alternator?

I agree with Don. You are way better off geting the correct alternator that has the L terminal for the fuel pump. If you don't do that, you are going to need something that tells the fuel pump to only run when the engine is running which would mean an oil pump pressure switch. The correct alternator is easy to find.