3g installed...still low voltage....help!!

dec322 · Jul 18, 2006

Well, I installed my 3g a couple of weeks ago and the voltage still dropped when I turned on the lights and things. So I bought the FFI 1 7/8 pulley b/c I have a smaller crank pulley (per the previous owner). I just put it on and I still have the same problem with voltage drop with accessories on. What have I done:

1. Cut room for 3g.
2. Run 4 gauge wire from soleniod to alt. with a 150 amp fuse.
3. Attach white wire using spade connector.
4. Used same plug on the other connector on the alt.

I haven't installed a 4 gauge ground yet....would this cause my voltage to still drop? Battery is brand new (2 months old).

Side note: I've had a problem with the oil pressure gauge dropping above 3k rpms. Since the 3g swap this problem has gone away. Weird, huh?

I've got new gauges sitting in the closet but don't have time to install right now.

Anyways....help with 3g please.

whtpny · Jul 18, 2006

I would say first to never trust your factory gauge. Put a multi-meter on the output of the Alt and check voltage. Then load the alternator and check again. Mine still moves a hair but when loaded it puts out 13.5 volts at idle with the lights. heater fan and fogs on. Bottom line........don't rely on that factory gauge.

HISSIN50 · Jul 18, 2006

Also make sure that the solenoid connections (and your fuse connections) are really tight.

Good luck.

dec322 · Jul 18, 2006

whtpny said:
I would say first to never trust your factory gauge. Put a multi-meter on the output of the Alt and check voltage. Then load the alternator and check again. Mine still moves a hair but when loaded it puts out 13.5 volts at idle with the lights. heater fan and fogs on. Bottom line........don't rely on that factory gauge.

I'll check it out tomorrow. I haven't even gotten a chance to drive it yet....just start it and turn the lights and heater (no a/c ) on.....

jrichker · Jul 18, 2006

The secondary power ground is between the back of the
intake manifold and the driver's side firewall. It is often missing or
loose. It supplies ground for the alternator, A/C compressor
clutch and other electrical accessories such as the gauges.
Any car that has a 3G or high output current alternator needs
a 4 gauge ground wire running from the block to the chassis
ground where the battery pigtail ground connects.
The 3G has a 130 amp capacity, so you wire the power side
with 4 gauge wire. It stands to reason that the ground side
handles just a much current, so it needs to be 4 gauge too.

dec322 · Jul 19, 2006

Today I'll be adding the ground.

I tested the output today before work and came up with this. At the battery before the car was started I was getting 12.5 volts. After I started the car the battery was at 13 volts. I then touched positive to the 4 gauge on the alternator and the negative to the negative on the battery....13 volts. Then I touched the soleniod (positive) and the battery (negative) and got 13 volts. Then I turned on everything in the car (lights, fogs, stereo, hazards, heater) and touched everything again....13 volts. Should it be higher? The tester I used was a little weird and didn't belong to me....the guy that owns it doesn't necessarily know how to use it. I'll put the ground on tonight and test tomorrow with a guy that knows his business.

Any input so far?

srothfuss · Jul 19, 2006

My car, (when running) with no load puts out:

14.5 volts at the alternator (all the time)
14.0 - 14.3 at the battery

When it's loaded with the heater and lights on

14.5 volts at the alternator
13.0 - 13.5 at the battery

Maybe since the ground is missing, the alternator is limited to a lower level output? We know that the alternator ground is via the engine and then to the chasis, so maybe without a good ground you are limiting the output?

68keyblr · Jul 19, 2006

srothfuss said:
My car, (when running) with no load puts out:

14.5 volts at the alternator (all the time)
14.0 - 14.3 at the battery

When it's loaded with the heater and lights on

14.5 volts at the alternator
13.0 - 13.5 at the battery

That's almost exactly what I get with my underdriven 130a 3g on my '68. In my case, at idle, I get about 13.2v at the battery with headlights on, PIAA driving lights on, and stereo thumpin. You should be getting above 14v at the battery at idle with no accessories turned on.

3g installed...still low voltage....help!!

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