Jetdriver69

Could someone tell me if the alternator sense line is in the 14 pin connector or on the fuse panel or both? After I cleaned up the fuse panel, my voltage is low across the volt meter and measured at the jumper terminal. I checked at the alternator and it is low there also. The battery tested good, so I want to check the sense line before I remove and test the alternator. Thanks.

Mrmerlin

the blue wire from the alternator runs through the 14 pin connector and goes to the CE panel;,
if your getting low voltage how are you determining this?
if by the pod gauge then you have a dirty ground ,
if with a volt meter ,
then you have a dirty connection and or a fried diode in the alternator or a worn brush

Jetdriver69

I checked the voltage with a multimeter and I was thinking it was a fried diode. Same thing happened to my 79 years ago. Funny thing is that the voltage was 13 volts plus until I cleaned up the fuse panel and cleaned all the grounds and 14 pin connector. Other than having a few wires chewed on by chipmunks, the fuse panel was really clean with zero corrosion on any blades or connectors. Just the normal 30 year slight corrosion on the fuses, which I cleaned with a dremel. Yes I had the battery disconnected and I am having the alternator tested tomorrow. But I think I know the answer already. Thanks!

Jetdriver69

I forgot to ask, exactly which wire on the fuse panel is the alternator sense line?

Mrmerlin

you need a WSM to find the wire,
or maybe Alan or Wally will chime in

Jetdriver69

Is it one of the three red, large gauge single wires located in the middle of the plug connectors at the bottom of the fuse panel marked Y or Z? If not, what are those three wires connected to? Is there any simple diagram other than the WSM diagram identifying what each multiple wire plug connects to? Every fuse/relay diagram does not ID those plugs. Thanks again. BTW MrMerlin, is that P-51 your's? Sweet looking bird!

Alan

Impossible to say without a model year...

Alan

Jetdriver69

Sorry, a 82 5 speed.

Alan

Z1 & Z6 & O8 are (linked) connections on the CE panel from the alternator to the dashboard. Black wire.

Alan

GlenL

I'm wondering what you mean by "sense line." There's an "exciter" circuit from the pod but otherwise it just measures the voltage in the pod.

Alan

'Sense line' is not the correct name - but I think its clear he means the exciter circuit - it's the only other connection to the alternator AKA (61) & D+

This is the rotor field initiator circuit - it has nothing much to do with voltage sensing in an alalog manner - but it does provide a basically digital indication of generation status...

Alan

Jetdriver69

Now that I have measured voltage at the battery and alternator, the pod voltmeter is measuring correctly at 11.3 volts. I was running off battery and the alternator is not charging. I am almost positive that the diode pack is bad, but will confirm today with a test under load at a alternator shop. Prior to me cleaning up the fuse panel, the alternator voltage at the pod would vary greatly from day to day, ranging from over 13.5 to less than 12 volts. Since I cleaned up the fuse panel and grounds, the alternator has quit completely, the fuel gauge stopped working and the temp gauge is now measuring accurately, go figure. Hopefully these are coincidences as the fuel gauge was intermittent before the fuse panel work and the temp gauge read high at the second white line constantly. The actual coolant temp was ok measured at the water bridge and radiator with a infrared gun. I measured EVERY connection on the fuse panel with a multimeter and all have good continuity, so I don't think the panel is the problem. Would the fuel sender not read properly with voltage less than 12 volts? The sender is less than a year old and installed by Roger, so I know that is good. If a new alternator doesn't fix the fuel gauge issue, I will remove and check the float and internal wiring. Any other suggestions? Thanks as always.

Mrmerlin

fluctuations with the voltage could also indicate worn brushes,
and the brush holder is replaceable.
a consistent charge of under 13.4 v indicates blown diodes

Jetdriver69

The alternator is being checked today, but the unit is only three years old. I know that doesn't mean anything, but for a Bosch unit to fail that quickly is pretty poor. I am installing a new stereo ssystem with amp, subwoofer, etc. Will the 90 amp alternator be sufficient to power everything and a 1200 watt peak 600 watt RMS amp. I will let you know the outcome.

dr bob

There's a current parallel thread with a lot of good advice on checking the charging system.


I'm going to speculate that you've managed to interrupt the connection through pin 1 of the 14-pin connector while cleaning and restoring. With key in the 'engine runs' position, this connection routes initial excitation current to the alternator field. The circuit is through the dash indicator bulb and a paralle resistor on the instrument cluster. If you open the 14-pin and measure volltage from pin 1 on the chassis side to ground, you should see battery voltage with key in run position. Plug the connector halves together, and measure from the exciter/field connection on the alternator to ground, and you should see a few volts with the key in run position. Both of these tests are with engine not running, just key in run position. If you don't see the voltage at the first test at pin 1, work back through the CE panel connections to find what's not working. If you do get battery voltage at pin 1 of the open connector but don't see anything at the alternator exciter connection, lift the connection at the alternator and test at the loose end of the exciter wire. It should be same as what you saw at pin 1. If not, there's an open circuit in the wire or the 14-pin engine side. If you see battery voltage with teh wire disconnected but it goes to zero when connected, it could be a poor connection in the CE or the 14-pin, or a fault in the regulator in the alternator.


The exciter circuit provides initial excitation, enough current to establish a magnetic field in the rotor (armature). With the rotor spinning, there's current available from the stator windings to provide excitation. The initial voltage at the terminal is a few volts, and the difference in potential between there and the positive bus is what lights the indicator by the voltmeter. Once the alternator is generating current, the stator voltage comes up, and through a few diodes is applied to the voltage regulator for use in the exciter circuit. With the exciter terminal now at battery voltage, there's no longer any potential difference across that indicator light, so it goes out.

With all this in mind, the indicator light should be on with key in run position but alternator not turning. If it isn't, it's most likely that the circuit path to the alternator is open someplace. It's also slightly possible that the regulator is DUFO, but your voltmeter test at the exciter wiring described above would discover that. Alternately, you can try grounding the exciter wire, with engine not running but key in run position, and verify that the indicator light comes on. No light means open circuit someplace between the the dash connection from the light and resistor, and that includes the CE connections listed by Alan and pin 1 of the 14-pin connector.