Packard Forum Index » V-8 (1955-56)

I'm hoping to find some guidance here. The generator dash light is off (or very dim) when idling, and it turns on or gets brigher when accelerating and driving at cruising speed. When the engine is off, my multimeter shows the battery with 12.5 volts; when the engine is idle or when I rev the engine the voltage at the batter drops to 11.76. The maintenance manual says this is normal function of the generator; however, the generator light should not stay on. This is relatively new - within the past couple of months. I haven't been too worried because the battery is not loosing its charge.

I've been reading about the maintenance manual on troubleshooting the generate and voltage regulator. I've inspected all the wires to the the regulator and generator; they appear fine (no cracks in the insulation). I cleaned all the connections to the regulator and generator. I also oiled the generator. This helped dim the generator light while driving, but it still is on.

What should I check, clean, and/or replace next?

It would appear the generator is not producing any voltage -- or at least an insufficient amount. Standing battery voltage is 12.6 so that part is normal. When the engine is running at a fast idle and above, specs call for an Autolite generator/regulator system to be adjusted to produce 14-14.6v and if a Delco system 13.8-14.8v. If you are only seeing 11.7v then the battery is discharging and nothing is being replaced.

To determine if the generator or regulator is at fault connect your voltmeter to the battery, run the engine at a fast idle and prepare to measure voltage. With engine running, ground the FIELD terminal on the regulator. Make sure it is the FIELD and not the GEN or BAT terminal that you are grounding. As soon as the FIELD terminal is grounded the voltage should jump to a number up in the teens which would be the maximum generator output. Only leave it grounded long enough to verify voltage does climb and to avoid blowing light bulbs be sure to close doors and check that any other lights are turned off.

If the voltage goes high with the grounding the generator is working and the regulator is suspect. If nothing changes then the generator or the field wire connection between the generator and regulator is suspect. You could repeat the test grounding the FIELD terminal on the generator to rule out wire problems.

Here is a simplified diagram showing how the indicator lamp is wired in the circuit. In a car the wires might be originating off any number of convenient but different places. The basic circuit connections and how the light functions will be the same. When the generator is producing voltage it is fed into the regulator on the ARM or GEN terminal, goes thru the cutout relay contacts in the regulator which will be closed over a certain voltage (typically they close around 1 volt less than the generator is adjusted to output) and then back out on the BAT terminal to the battery. In that instance the light will be out because both sides of the bulb are seeing the same voltage. If the voltage coming from the generator on the GEN terminal is not enough to close the cutout contacts the battery voltage will be the higher value and the lamp will be on because it is either getting a solid ground or seeing a lower voltage from the generator so the difference in potential will flow thru the bulb. At slow engine speeds the generator may not produce enough steady voltage to keep the cutout contacts solidly closed so the bulb might flicker. At faster speeds, in the instances where the generator is outputting a steady higher but not quite enough voltage to close the cutoff contacts, with the contacts open the bulb will be on but dim. If the engine is not running or generator is producing voltage significantly lower than battery level it will be bright.

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I just had the same problem. My Gen Light was on. I checked the battery, it had 12.3V. I revved the engine and still had 12.3V. I replaced the voltage regulator that I got from NAPA and now when I rev the engine I get 14.3V.
I have a 1955 Clipper, positive ground but same results.
Don't forget to polarize your system, that is:
Before starting the car:
Obtain an 8 inch piece of 16 gauge or larger jumper wire.
Momentarily (no longer than 2 seconds) touch the jumper wire to both the armature (ARM) terminal and the battery (BAT) terminal. There may be a brief spark; this is normal.