1971 Cutlass S
461
3-speed
no gen dummy light

Problem: Charging system was not happy. Car never read 14v and with the lights on read 10-11 at best! stopping for gas after even a 20 minute drive was not an option as I wouldn't have enough juice to start it again sometimes.

What I did: I wanted to replace the seasoned 3 wire alt with some more power as i plan to upgraded the sound system in the near future. I did not want to rely on the 40 year old original wiring though so I went for a 100 amp 1 wire capable Summit alt on the car. I believe the old alt was only 63 amps.

Outcome: 14 volts! BUT when the headlights come on the volts drop to 12. Lights off and just the turn signal on the volts drop/fluctuate with each blink 1-2 volts. the seems to run better even, exhaust doesn't smell rich anymore. EDIT: it did this same things before with the three wire setup/old alt. The old alt just never made 14v on the gauge.

Now by the looks of this new alt, (link again),
it looks like it could be wired like a 3 wire as it has the field and sensing tabs. I just had major concerns about the higher output alt running through those old thin wires.


QUESTION: What can I do to solve my voltage drop issues? I experienced the volt drop issue with the previous 3 wire (figured my external regulator was on its way out) and now the new 1 wire. Would running a wire from the sensing tab to he terminal battery post on the fender help the alt realize the volts are low with the lights on? Or should i just hook it up as a three wire and keep my fire extinguisher close by?

 

I continue to be mystified by the people who buy one-wire alternators. There's a reason why GM never installed one from the factory.

I don't know what your aftermarket alternator will do if you wire up those terminals, as it obviously doesn't use a factory style regulator. Personally I would have gone with the 94A 3-wire 12SI from a 1986 Caddy Fleetwood with the Olds 307. New price from RockAuto about half of what you paid.

 

I appreciate the time you took to respond, I really do but ugh...1 wire capable, capable...it is not a 1 wire tractor alternator and I can hook it up with my existing factory loom, might have to change the r/l plug style, but there are cheap conversion wires for that. I'm just worried about the factory wiring burning up on me and I wanted to rule out the external regulator so I wired it up, ATM, as a one wire alt. If i do wire it up with the factory connections I will have a regulator redundancy.

I'm just gonna play devil's advocate cause I have nothing better to do at the moment - and again I appreciate your post.

• I don't have an idiot light
• I don't care how many wires i have in my engine bay
• I don't care if i have to hit 1100 rpm as i hit that in my first 10 feet from a stop anyway and it continues to charge until i shut it down. At least that was my experience today on my test drive sitting at a dead stop in center city Philadelphia traffic for at least 15 minutes.
• I would be willing to bet they didn't try to reinvent the wheel and the internal regulator is nearly, if not, identical to every other 10SI internal regulator that came from the various factories over the past 2-3ish decades.
• Rock Auto unfortunately does not provide the the 86 Fleetwood's 307 alternator during a standard search for a 71 Cutlass. That 307 caddy's alt costs 65$, then core charge for $22 (because I don't drive an 86 Fleetwood 307 and even if I did it would cost at least half of that to ship it back not to mention the hassle of driving to USPS) then the 8$ for shipping and were all in at 95$ for a less than visually stunning unit. Well for 100$ I have a chrome unit and if the quality of the chrome is only worth the extra $5 I have in this then I'm OK with that and expect the quality that I paid for.

I'm really just trying to understand the drop in voltage that I experienced with the old alternator and that I still experience with the new alternator. It may be that the old alternator was simply on its way out as it couldn't even supply 14v per the gauge. It could be that the regulator was on its way out. It probably, however, just that the fact that the headlights do draw that much and the internal sense wiring still reads 14.0-14.4 at the alternators output terminal because it more than likely is.

I'll more than likely hook up the sense terminal to the switch and not just the batt terminal on the alt to see if it works as I would expect. Possibly even reducing or eliminating my voltage drop with the lights on. That would be the best outcome from my perspective, I avoid the small diameter factory power wires with my 4g alt to bat wire and still allow the alternator to sense low voltage in the system and increase output to accommodate and lows due to heavy accessory use. I will report back within the week.

again though i have to say i hope this comes across without any negative vibes - just typing away my thoughts and my perspective as to why i chose the alt that i did.

 

Check all of your connections make sure yours is clean and you have good grounds..also verify with another voltage gauge if possible. I have had the summit chrome 1 wire connection alternator since 2002-03 and it works perfectly..even put a 50% underdrived pulley on it..it will run my MSD box, 300 watt audio amp with lights and will not drop below 14 volts. Here is a photo at idle reading 15 volts..hope this helps.
Sean

 

Forgot to add Holley electric fuel pump.

 

and it sounds like you have it wired as a 1 wire, correct?

I did add a new braided strap from the alt to the intake after I still had the voltage drop with the new alt, even though I'm sure that bracketry was enough, but the issue remained. I'll check the firewall and other grounds again, reapply dialectic grease if need be, but i don't expect to see any corrosion.

mechanical FP for me. I do have some feedback in the radio with RPMs, ill check that ground too. Hell ill just go through them all while im digging around.

 

Correct just using single wire. In picture you can see the GM block plate still on the alternator never removed it. And using original fuse box wiring.
Sean

 

There are a couple of things that you need to look at. Your problem is almost certainly due to excessive resistance in the connections between the alternator and the voltmeter. The two most likely problem locations are the terminal stackup at the horn relay junction stud and the ground path from the alternator to the block.

Remove all the wires from the stud on the horn relay and clean them to shiny metal. Run an auxiliary ground strap from the alternator rear case to the block. These two things should help a lot.

It is unclear if running a sense wire will have any effect. The problem is that most one-wire regulators have the SENSE and FIELD terminals connected in the regulator, so the SENSE terminal is essentially monitoring the voltage directly at the regulator. Obviously this can't possibly account for voltage drops in the harness. Simply adding a sense wire to your existing regulator won't help, since that internal connection is still in place. Voltage will take the path of least resistance, which is the internal connection between the SENSE and FIELD terminals. Some regulators, like the one in the photo, have an external tab for this connection, others do it in the regulator body. If yours has the tab, you can try to cut it, but that turns your one-wire alternator into a three-wire alternator. Your call...