Ok here's my dilemma. Just got the 388 stroker running in my 72 chevelle and the battery isn't charging as it's suppost to. I'm running a 50% underdrive Moroso crank pulley (which I'd like to run if at all possible) along with a Moroso Water pump with stock pulley and a Proform one wire alternator 100 amp alternator from Summit. I originally had the one wire hook up only but I just changed it so its a three wire now.

So right now the main power wire is hooked up to the starter, the left wire on top of alternator is hooked to power wire terminal on the alt, and the right wire is hooked to the access. switch on the fuse box. Battery is in the trunk with a good ground. I hooked up the battery to a volt meter which is showing around 12.4 volts, which I believe is not enough. I eliminated the external regulator due to being a one wire alt.

While reving, the lights will go brighter, but at idle they will go dim and eventually die out. graemlins/sad.gif

Any help would be great. Thanks

The advantage of a 3 wire alternator is that it remote senses voltage, usually at a terminal where heavy load is taken from like early horn relays.
If you hook up the sensing wire of the alternator to a terminal in the engine bay where a hi electrical load is taken off, this will tell your alternator to ramp up voltage to meet the need of that load and will keep your headlites brighter.
Here is a link to a site that has allot of good electrical info, very good Tech articles that explain voltage sensing and voltage drop

http://www.madelectrical.com/electrical-tech.shtml

I assumed you measured the alternator output and took a reading??
1, How large is the gage of wire going from the battery to the starter?
2, How large is the gage of wire going between the alternator and starter.
3, Where is the forward lamp harness wire tied in? Originally there was a wire from the alternator to the horn relay and that wire tied to the forward lamp harness wire.
Sounds like that jumper wire to the back of the alternator needs to be tied somewhere else, but not sure where to suggest yet.

I have my alternator wire hooked up to the starter. A couple other wires are hooked up to the starter as well... power to fuse panel, msd 6al box, and battery cable.....I'm thinking it's the underdrive pulley but I'd like to keep it on and make this setup work....any suggestions?

What's the voltage reading on the back of the alternator?

I'd also bet it's the underdrive pulley. With the stock pulley that alternator is probably only capable of 40A at idle. When you put on that underdrive pulley you will get 10A at idle if you are lucky because it's not a proportional change with rpm.

You need to run the sensing wire to the big power wire coming up to the starter with a seperate wire. That's the only way to get the remote voltage sensing working correctly.

Peter

John Muha....just tested the volts and it's only putting out around 12.2 volts at the alternator.

Peter, yeah I'm thinking it's the underdrive pulley as well...is there a tool to take off the cracnk pulley because after trying to get it off today, it doesn't seem likes it's going to be that easy.

Also...there should be a way to keep my 50% underdrive pulley and still get the 14.2 volts...right?

I have the same problem on mine, with deep groove pulleys installed. The alternator, which I've used previously when the engine was a 327, always kicked in at 1400-1500rpms.After the change to a BBC with the deep pulleys, I have to rev it to about 3000rpm to kick in.It'll stay charging for a minute or two at lower speeds, but then drops out until it revs up again (I'd like to know why that occurs).A couple of guys in my group now have similar problems at the track, and are charging off of my generator between rounds.I've heard of a low-rpm cut-in alternator, but can't seem to locate the real info on it.Maybe the best solution.

The jumper wire that you have tied to the aternator terminal on the rear. That's the remote sense line. Like Peter said. Disconnect this jumper wire from the alternator stud and run it down and tie it to the starter. Disconnect the battery before you move wires.

You could also try and put a smaller pulley on the alternator only, allot of alternator/starter rebuild shops will have a selection of available pulleys to fit. This smaller alt. pulley should help you recover some of the lost RPM from the underdrive crank pulley and should also help keeping voltage up a low engine speeds.

Your not having any cooling problems at idle and in slow speed driving underdriving the water pump??

I'm going to try to get this pulley off and just put the stock pulley back on..We'll see what happens.

You have to undo the 3 bolts holding the pulley on and remove the center bolt holding the balancer on to get the pulley off. Then, it should drop right off.

Peter