Thread: Classic Alternator Issues

Originally Posted by PeterAllen

Hope someone can guide me on this one.
I have replaced my Alternator and when installing mistakenly connected the wiring for the tacho to the wrong connection point. When I tried to start the car I have shorted something out but can't seem to find what.
Car won't start, I have spark at the coil. The tacho wire seems to go to the coil +ve terminal but I could be wrong on this as it is the same colour as a bunch of others that run through the same harness. The haynes manual for the wiring doesn't show much and haven't been able to track down better wiring diagrams. The car is a classic EFI 1987. The ignition amplifier is under the coil and not on the distributor. Any assistance would be appreciated.

What is the tacho wire doing at the coil +ve? There should be a white wire with a black trace at the coil -ve, that is how your computer reads firing pulses. The tacho is a white/grey trace wire connected to a special field terminal at the alternator, and has nothing to do with the running of the engine. The brown/yellow trace wire is the charging bulb wire to the dash, should be connected at the alternator field.

Ouch.
The wire to coil NEGATIVE is the wire that tells the ECU that the engine is running and the revs.

By connecting to the positive you have either burned out the diode which is in series or you have damaged the ECU.

Maybe check if the diode is open circuit and if it is replace. Otherwise see if it starts with another ECU with the wire connected to NEGATIVE.
I think it may be time for an auto elctrician or LR specialist.

.Regards Philip A

Thanks for your info.
Do you know what I could have blown by connecting the tacho wire incorrectly.
Do you have a wiring diagram of where the tacho wire from the alternator goes to?
My alternator only had three wires to connect, The main power from the Starter soleniod, the battery lamp warning light and this tacho wire.
Regards

I ran a test from the Battery +ve terminal to the coil -ve and had a reading of 12.5 volts. Haynes manual said it should be 0.
Why would I be getting spark from the coil if I had stuffed up the ignition module etc.
Where is the diode located and how do you test it?
regards

Originally Posted by PeterAllen

I ran a test from the Battery +ve terminal to the coil -ve and had a reading of 12.5 volts. Haynes manual said it should be 0.
Why would I be getting spark from the coil if I had stuffed up the ignition module etc.
Where is the diode located and how do you test it?
regards

The coil -ve voltage is controlled by the ignition amp, it is variable as the engine fires. When stationary the voltage should be the same as the +ve terminal, otherwise you have shorted the coil -ve with something. As you have spark this is not the case. Did you read your voltage with the ignition on or off?
The diode should be strapped to the loom near the coil. (I think). Read its resistance, should have a low resistance one way and high with the meter leads reversed. It should have the white/black trace wire connected to one end.

I tested with ignition off as stated in the book.
Thanks again for your comments.
Regards

Thanks for your info.
Do you know what I could have blown by connecting the tacho wire incorrectly.

Car won't start, I have spark at the coil. The tacho wire seems to go to the coil +ve terminal but I could be wrong on this as it is the same colour as a bunch of others that run through the same harness. The haynes manual for the wiring doesn't show much and haven't been able to track down better wiring diagrams. The car is a classic EFI 1987. The ignition amplifier is under the coil and not on the distributor. An

The tacho wire goes to the "W" terminal on the alternator. It reads from a field of the alternator. If you have a look at the back of teh alternator it should have "W" stamped there.

The ECU engine revs sensing wire goes to the coil negative.


You seem to be mixed up on which wire is which, at least I am .LOL. The tacho wire will be with the alternator loom and the ECU wire should be on the Air Flow Meter loom. ie completely different places.

I am assuming that you have placed the ECU sensing wire on the + of the coil rather than the -.

The tacho wire should not affect anything to do with starting, even if joined to 12v, I think it would just destroy the tacho, but it may have blown a fuse that also controls some other circuit.

The ECU sensing wire on the other hand may have caused problems in your ECU.
Regard sPhilip A

G`day Peter,

The white/slate tach wire goes to the mutifunction unit ( has another name also ) , It is in the binical ( instruments ) .

Not a fan of haynes but do you have above 12volts with ignition on , yep .

The tests for the under coil amp are a little different to the other amps , don`t remember exactly what , have to look in the book if needed .

If your saying you have a good regular spark from the coil lead when the engine is turned over , the amp , ect . should be good .

Take the cap off , hold the coil lead around 3mm above rotor arm and rotate the engine , if you have a spark the rotor will be crook .

What else did you do at the same time you replaced the Alt ? Have you upset something else unrelated ?

Check the wires coming out of the dissy , mostly the connection that runs near where you were working .

Check all the normal things like the fuel pump running a little ( seconds )/relays tripping etc when the key is switched to On /ignition/start etc .

Is it dual fuel ?

Cheers