vze2jshn

When i start my'78 OB volt meter reads low and battery light is on and hot post reads only 11 volts or so. When I rev engine once or twice red light goes out and post reads 13.8 volts or so. After this everything is OK at idle, etc. This only happens when I first start the car. Checked threads but don't seem to see this particular problem. Recently installed LED back lights in pod. Could that be related to this problem or just coincidence? Any suggestions greatly appreciated.

jeff spahn

Check your 14 pin connector and see if all of the connections are being made. if your 14 pin connector is fine, perhaps your alternator is going. It could be an exciter problem.

WallyP

There was a running change to install a 68-Ohm resistor in parallel with the red light to increase the alternator field current (exciter circuit) so that current generation would start earlier. If you don't have the resistor, or you have a faulty connection on the resistor, you have to rev the engine to get the alternator kicked on.

vze2jshn

Thanks guys. I have heard of the exciter situation but did not notice a resistor on the back of my original '78 pod. If it is a later addition where do I get the appropriate resistor and where/how do I install it? It's a bit strange that after all these years (have had car since '86) this should emerge now.

WallyP

Probably just a build-up of resistance in the many connections found in the exciter circuit. A good cleaning and treating of the connections would probably solve the problem.

The resistor is nothing special - any 68-Ohm 5-watt resistor will work - but you probably already have one. They are installed on the back of the voltmeter, across the terminals for the warning light.

Landseer

They added the resistor, but reduced the wattage of the bulb.
Both systems have the same target resistance, inducing the same current at the alternator.

So, other accumulated resistance might be the problem.
Am assuming this is new behavior, btw

But, also a brush can hangup in the alternator. Had this happen on a bosch for an 86.
Started out occasionally on startup, quickly correcting itself with revs.
Progressed to an apparent non-charge situation a little more constently.
Then, hung completely so that a little hammer tap was needed to improve charging.

(Am speculating on the brush --- could have been a circuitry problem in the alterantor --- I'm assuming here)

Tiny tap while car was running --- you could hear the engine drag as the alternator kicked-in full.
Went through that cycle 3 times before I replaced the alternator.
Light was OFF in most cases when this apparent partial charging was going on.
That threw me.
When battery charge depleted during a long trip to a threshold around 10, the whole dash would flash, as noted in the literature for the warning system.

So, something like that is another possible failure mode for the charging system in my experience.

vze2jshn

Problem new-just started presenting. I May install another alternator I have to see if the alternator is the problem and also check all connections, although top of engine wiring harness (Fausett) is about one year old.

Landseer

Alt exciter runs through 14 pin, I think pin#1? Have seen broken solder joints within the 14 pin connectors before that make intermittent contact.

Don't mean to derail the path you were going down. My post reads pretty strongly next to the known-wisdom grounded posts of Wally. Take mine with a grain of salt, but I did see the behavior noted.

vze2jshn

Will check all connections beginning with pod card connections - had pod off prior to this problem - before I try alternator change.

Alan

The light indicates no charging - so is not actually directly related to a low voltage level ... though that is common.

If the light is on at startup and goes off after revving - as the voltage rises - then it seems the connections are correct (else light would stay off). Resistance build up would likely give you a dimmer light... Seems most likely you do in fact have an alternator issue or a connection/damage issue with the exciter resistor (since you were in the pod this is also a possibility).

You can temporalily test for the resistor theory with any 68 ohm resistor added in parallel to the exciter line to the alternator (say at the 14 pin connector) and the battery jump post after starting and before revving it - does it kick in the alternator? Just don't leave it this way

If this doesn't help I think its conclusively an alternator issue...

Alan

tmpusfugit

While all the checks suggested above make sense my own limited experience with a couple of alternator failures in the last year, suggest the alternator itself...both alternators failed with symptoms like yours. No charge when the car is started, then increasing rpm's to say 1800-2000 will excite the alternator, but even as it charges the voltmeter will read a lower voltage than in the past. One of my 2 failures ran this way for 60+ days before it failed completely (^$^#^^ rebuilt alternator) The other I replaced before it failed completely. It is difficult to do a reliable post mortem on these, but, the one still working had one defective diode (of 15) and the alternator that completely failed had chewed up brushes as well as 2 failed diodes in the circut.

An observaton that may not be relevant at all....around here there is a lot of sand on the roads. If these S cars are missing the belly pan and the alternator shroud, the alternator collects a lot of grit. Has to be bad on brushes, and neither of my cars had the belly pan or alternator shield when received. My one remaing car now has both....

Landseer

Good point.

A little OT, but on a rescue, its good to pull the hose off the alternator and use a vac.

Mice will leave nuts in the hose and the pieces can jam in the rotating alternator and rip apart circuits, at least on the Rhone alt.

vze2jshn

Could not locate a 68 OHM resistor at auto zone or radio shack may try Napa tomorrow. Took alternator off and had a friend who owns an alternator/starter / AC/ hydraulic hose shop put it on the tester--all diodes OK and exciter circuit in alternator OK--his test light went out. He says it must be the exciter wire(s) to alternator. I put alternator back on and with ignition switch on blue wire when connected to alternator reads ~ 2volts. Same wire connected to alternator with car running and battery light on reads 0.63 volts so I guess I have to go back to 14 pin connector and on to pod to find the problem? Anyone know what the above readings should be? Thanks again for all the assistance.

vze2jshn

Took pod off to check resistor situation--no resistor to be found ('78 OB) and wsm wiring diagram does not show any. Upon further inspection I realized that the battery icon/ exciter bulb also serves as one of 4 back lighting bulbs which I had replaced with wedge LEDs. Re-installed incandescent bulb for battery icon and, voila, battery light goes out and alternator puts out 13.96 volts at start idle (thank you to whomever had mentioned that LED bulb will not act as exciter circuit which I read as I perused the threads) otherwise I'd still be spraining my brain. Also thanks to everyone else who provided a tutorial on this subject. In summary it seems the bulb sans resistor acts as the exciter for the alternator on my '78 # 342. All the best, Greg.

Landseer

It actually has to be on a separate circuit completely from the back light bulbes, due to the voltage cancellation aspect, but if it was LED that's a great answer to the problem

Congrats.