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Discussion Starter · #1 ·
This is a puzzle and I'm looking for help.

It has rained alot here in the last month and son drove through a big puddle and he says all the dash lights went on.

Within a week the battery was dead and everything pointed to the alternator.

I replaced the alternator and everything worked fine for a week.

Then dash lights came on again and engine died. Dead battery...

Troubleshooting said bad alternator.... everything ran fine with 13.8+ volts at the battery. 2 hours later the lights are back and the battery with engine running is 11.7 volts...

Seem alternator is not working again.

I have done some research and it seems the regulator might not be "waking up" via a signal from the "dash light" .... not sure what this is as the internet, as usual, is not well versed on this issue.

It seems when the start sequence is initiated voltage is sent to the alternator to wake it up and tell the regulator to start charging.

My question is what voltage should I have on which of the two wires going to the alternator plug (two wires).

I can't find a good schematic of the full charging system to see where those wires go and what the voltage should be. HELP EC!!!
 

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The signal wire is light green with a red stripe (LG/RD) and should be whatever voltage the battery is at with the key on engine off.

Here is a description of the charging system from the manual:
Functionality (Duratec engine only)
With the ignition switch in the ON position, voltage is applied through the warning indicator I circuit 904 (LG/RD) to the voltage regulator. This turns the regulator on, allowing current to flow from battery sense A circuit 112 (BK/YE) to the generator field coil. When the engine is started, the generator begins to generate alternating current (AC) which is internally converted to direct current (DC). This current is then supplied to the vehicle's electrical system through the output (B+) terminal of the generator.

Once the generator begins generating current, a voltage signal is taken from the generator stator and fed back to the regulator internally. This voltage feedback signal (typically half the battery voltage) is used to turn off the warning indicator.

With the system functioning normally, the generator output current is determined by the voltage of the A circuit. The A circuit voltage is compared to a set voltage internal to the regulator, and the regulator controls the generator field current to maintain the correct generator output.

The set voltage will vary with temperature and is typically higher in cold temperatures and lower in warm temperatures. This allows for better battery recharge in the winter and reduces the chance of overcharging in the summer.

Battery Positive Output Circuit (B+) 36 (YE/WH)
The generator output is supplied through the battery positive output (B+) terminal on the back of the generator to the battery and electrical system.

I Circuit 904 (LG/RD)
The I (ignition) circuit is used to turn on the voltage regulator. This circuit is powered up with the ignition key in the RUN position. This circuit is also used to turn the charging system warning indicator on if there is a fault in the charging system operation.

A Circuit 112 (BK/YE)
The A circuit or battery sense circuit is used to sense battery voltage. This voltage is used by the regulator to determine generator output. This circuit is used to supply current to the generator field (rotor). The amount of current supplied to the rotor will determine generator output.
 

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Discussion Starter · #4 ·
Update:

I check voltage at the fuses and had some variation. 12.3 at bat engine not running. 11.75 at the 15a fuse in the battery junction box and 12.3 at the 10a fuse in the accy fuse box (kick panel). SO I tried starting the car and it started fine. No lights. I check the bat voltage running and now it has 14.3+. Alternator working again !!!!.

I took the bat to the store and had it checked. They said it needed a charge... 30 mins later they could not get any reading off the battery to even start the test... WTF!!! Bought another battery thinking maybe an internal short was loading up the alternator and overheating it.

New battery in, started fine, 14.3 at the battery when running, alls good, then I turned the lights on and the AC to see if the voltage changed. Still holding over 14v. GOOD then the bat light came on!!! flickered at first then after a bit full on brake light too. Voltage at the bat is still 14v running!!!???

This is where I'm at. Something is telling the charging system is not working but it seems to be working based on voltage readings.

Squishy any ideas?
 

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Is the alternator a rebuild? Probably so, but just going to say that the cheapo diode banks that are loaded into the alternator on a rebuild are incredibly cheap. Maybe and internal thing with the alternator. More specifically, with the diode bank. I also wouldn't rule out your grounding or wires... many, many things to check. I know wires don't wear out, but sometimes there are breaks in them from date of mfg to the present for whatever reason. Continuity checks not with standing either.
 

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Going by the diagnostic charts, if your symptoms are that the indicator light is on while the engine is running, but the charging system voltage still increases, it wants you to try disconnecting the 3-pin connector from the alternator and check the warning light with the key on engine off. If the light still illuminates, then the only cause listed is a short to ground in the LG/RD circuit.

The brake warning indicator also uses a LG/RD wire to the DRL module and parking brake switch, but it's in a different connector and don't seem to be related. I don't know much about the electrical system so I'm not sure why they would both be on, other than maybe a short inside the instrument cluster itself.
 
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