After replacing by a mechanic the alternator on my 82 5 speed due to a nasty pot hole strike, the alternator will not excite nor will the alternator red light in the gauge illuminate with the key on. Insurance is paying the bill so Im not doing the work.

Voltage at the post is around 12.5 volts with engine running and with all accessories on approaching 10.5 volts but no red light. I charged the battery last night and the interior voltmeter is now showing over 13 volts from a fully charged battery.

Is this a simple blue wire connection from the alternator to the #1 pin on the 14 pin connector? If the blue wire has continuity, then I have read it may be the red light bulb itself or the gauge resistor that has failed?

If the blue wire is not connected or bad, would this cause the red alternator light not to come on with the ignition switch to ON?

If the bulb and/or resistor is bad, is there a tutorial for its replacement or just follow the "pod removal in 15 minutes" write up.

Thanks!

 

If it was a later alternator install you may need to change the resistor on the back of the cluster

 

At pin 1, you should read battery voltage with your meter with key on, engine side of the 14 pin removed. If you have this, ground that lead and your red light should be on. That tells you that the car, side of the system is OK. Then go after the circuit to the alternator with your meter.

 

If the blue wire isn't connected to the alternator (or is broken somewhere) the charge light will never come on.

Given what happened - I'd not be looking in the pod - the damage will most likely be near the alternator - but testing at the 14 pin (per Dr Bob) can easily confirm this.

Lots of folks remove the alternator and dangle it from the wires... (esp. for regulator changes) this is a no no - the blue wire is always the one that breaks.

Alan

 

check the bulb

 

Only check the bulb in circuit as Dr Bob already noted above.

BTW - I'll bet this one isn't the bulb (it virtually never is anyway).

Alan

 

My bet is the blue wire too.

Same thing happened after the engine rebuild, OEM alternator wouldn't charge. We tested the alternator before looking for a break in the wire. Of course the wire was frayed and had to be spliced after confirming the alternator was good.

Will check on Monday once it is up on the rack.

If it is the bulb and/or resistor, I assume they are available from Roger?

 

Don't worry about it - that is extremely unlikely. It is well protected and nothing you can do at the alternator stresses it any more than normal - which is much more than can be said for the wiring to the alternator.

Alan

 

just had to replace my bulb. when bulb went out, no power to alt exciter.

 

On a '78 you have only a bulb - unless it was ever updated. Whilst the bulb is still usually pretty robust, later cars have a bulb and 68 ohm resistor in parallel - either alone will initiate the alternator (although at higher than idle RPMs). So if it doesn't start generation even at 3K RPM or higher it's always most likely to be a connection problem. Earlier cars with the flex PCB's also suffer from pod connection issues - especially after they have been worked on a few times... later cars with rigid PCB's are more robust.

Alan

 

The pod bulb leads a very easy life. It passes current only during the short period (sorry...) while the key is on and the engine is not spinning fast enough for the alternator to generate its own excitation. In the giant scheme of bulb life tests, this one has it very easy. Later cars (I think starting around '82-'83) have the resistor in parallel with the bulb, so current demand through the bulb is reduced somewhat.

The diagnostic method I recommended has you test for voltage at the 14 pin connector pin 1, with the engine side of the harness disconnected. Meters are very high impedance devices generally, so you'll see battery voltage at that point with key on if there's a path through either the bulb or the pod resistor.

For Bosch alternators, having either the bulb or resistor fail will not prevent the alternator from charging, but it may require a higher initial engine speed to get the self-excitation started. ~~3000 Engine RPM is the number kicked around for that requirement.

To test the light, grounding the #1 pin in the 14-pin connector with key on provides a current flow path through the bulb (and the resistor) to ground, and should light the bulb. If you passed the voltage test above but fail the bulb test here, your resistor is OK but the bulb has failed.

With the14-pin connector assembled, and with key on, you should be able to duplicate both the voltmeter and bulb tests above, using the excitation lead at the alternator that's now connected through pin #1 at the assembled 14-pin connector. Do the tests with the excitation lead disconnected from the alternator. If you passed the voltmeter test at the 14-pin but fail at the disconnected alternator excitation lead, you have a failed "open" wire somewhere in the FOE (Front Of Engine, my nomenclature) harness. If the charge light in the dash is ON with nothing connected to that excitation lead, your FOE excitation wiring is damaged, and is passing current through another circuit in the harness. That would be insulation damage, and a chance to explore the innards of the harness. Remember that these tests are done with the excitation wire DISCONNECTED from the alternator, ignition key in the ENGINE RUN position.

 

I have the same issue, where I thought it was my bulb test circuit, but Alan and others lead me to this circuit. If I rev the engine, the alternator kicks in and all of the caution lights go out. It happens on most start ups and I have to rev the engine to 3k to get the lights out. Does this have to do with the bulb and 68 ohm resistor mentioned earlier in the thread?

 

I always thought that cars prior to 82 fitted with alternators made by Paris Rhone/Valeo required the change of resistor to ensure the excitation of the system at low revs. This is when the old type of alternator was upgraded to the Bosch type. This car had the alternator changed - see first post.
Just my thoughts because I am electrically challenged at the best of times.

 

This is correct - you need a lower resistance for the later alternator on early cars.

All but the early cars 78-82 should already have this stock, An '84 should have it.

Alan

 

Well if the bulb works in bulb test mode and is on when the alternator doesn't start up (voltage around 12v) and goes out when it does (voltage around 13.5+v) then certainly the bulb is there and the circuit connected OK.

It's possible that just the resistor connection is bad (quite rare) Or that the regulator has a problem.

With the 14 pin engine connector disconnected - ground the blue wire on the car (fixed) side though a DMM in current (10A range). With the ignition on you should see the charge lamp illuminate and the current should be about 0.1A for the 1.2W bulb alone but 0.3A if there is a 68ohm resistor in parallel.

You cannot measure resistance directly here as the bulb filament resistance varies by a ratio of approx 10:1 depening on if its hot/cold

Alan