Running Voltage is 11.3

[John 69 Camaro]

Hi,

My running voltage dropped to 11.3 from 13.5 after I reassembled the car from my winter project. I removed the factory AC & Heater and just blanked off the firewall opening. I also installed a DSE 7-speed wiper and a transmission temperature gauge for the 700R4.

I used a relay for the wiper motor and taped into the 18 gauge yellow wire in the engine compartment as my ignition source. I tapped into the BAT connection in the original fuse block for the positive feed. All worked well on installation.

Since I have a large Delco Distributor I tapped into the original resistor wire in the engine compartment that originally went to the coil as my ignition source.

When I finished installing the fender and front end I fired the car up and noticed I am only getting 11.3 volts from my 100 AMO Delco alternator. Last seaon it was putting out 13.5 volts. I disconnected the wiper motor and transmission temperature gauge without any improvement. I then disconnected the negative battery cable and placed an ohm meter on the positive cable and the negative cable to ground. The reading follows:

a. Zero ohms with all circuits closed.
b. 2.5 ohms when I open a door.
c. 0.8 ohms when I turned on the headlight switch.
d. With the door opened and the iginition switch on the reading was 2.5 ohms; however, when I closed the door the ohms jumped to 180 and settled around 30.

Are these reading normal or do I have a short somewhere?
Is it possible my alternator is bad?

Any advise on this problem will be greatly appreciated.

John

[willih6996]

Give this a shot to see if the alternator is good or not. You are going to need a digital multi-meter. You can also go old school and start the vehicle and pull the positive battery cable off, if the vehicle stays running then the alternator is doing its job, but if it shuts off it could be bad. That is really not the best way to test it.

The other thing is to make sure that you have a ground running from the motor to the chassis, the chassis to the battery and a thick enough lead going to the alternator. Honestly I think you have some sort of ground issue.

A lot of car stereo guys bump up the positive lead to the back alternator to also allow the rate of flow from the battery Positive voltage in, to the same rate of flow to battery ground going out.

This is out of a FLUKE Multi-Meter Owners Manual.

Testing Ripple Voltage on an Alternator
Ripple voltage or ac voltage can be measured by
switching your meter to ac and connecting the black lead
to a good ground and the red lead to the “BAT” terminal
on the back of the alternator (not at the battery).
1. Insert the test leads as shown in Figure 13.
2. Set the rotary switch to K.
3. Touch the red probe to the “BAT” side of the
alternator and the black probe to ground.
4. Read the display. A good alternator should measure
less than 0.5 V ac with the engine running. A higher
reading indicates damaged alternator diodes.

Check out the PDF below
PAGE 45 is Figure 13. stated above in line one.

23711

[paul67]

Check your grounds I only missed 1 and it caused this.

[John 69 Camaro]

Thanks guys. I removed the alternator and had it tested and it was putting out 100 AMPS. After I installed it I checked to ensure I had a good ground at the alternator, as well as ignition voltage going to the FI lead. Both checked out okay, so I replaced the BAT terminal stud going to the alternator because it was corroded. After getting the serpintine belt connected I fired it up and the voltage was 14.1. So I figured I had too much resistance at the BAT terminal or a bad alternator ground or both. After that I cleaned all the 10 gauge terminals from the terminal block to the horn relay. Hopefully the problem has been corrected. Thanks again for your help and the pdf is very informative.