Hello, Having trouble diagnosing a no charge condition on my 1987 f150 with a 302. Today I started the truck to find the battery light on, checked the voltage at the battery and it was around 12.5. The alternator was replaced about a month ago. I checked the output at the alt and find nothing but Battery Voltage. Its easy enough to take off so I took it and my receipt to advance and they tested it and said it was OK. So I then looked at all of my connections and everything seems fine. I'm still thinking the Alt or reg are bad, they said they tested the output of both. My question is which wire/wires should I check to check the regulator? Its mounted externally on the back of the alt. Total,I have two plugs with six wires, 3 on each. To the Alt The Blk/org I have battery volt, coming from the VR I have less than BV with the engine running but I want to make sure I'm checking this correctly. Any help?

 

I've had 3 different "oddities" like this over the years...and each time it was something different.

One time it turned out that the battery posts and the cable ends needed cleaning. There wasn't any buildup on them, but once I used a cleaning tool on them, everything was was OK.

The second instance I needed to replace both of the battery cables. The ends looked fine, but the copper strands inside covered by the insulation on them was pretty bad.

The other time turned out to be a combination of a dirty ground to the frame connection and a loose ground wire on the alternator.

Also check the connections on the solenoid just next to the battery.

12.5 vdc is a little low IMHO...should be around 12.9. Try removing both cables and then check battery voltage.

I hope this helps you...and good luck.

 

What Vern said! Had intermintent charging issue. I had a loose/dirty engine ground. Cleaned it up and tightend and all was fine.

 

Have your battery tested.

 

I will go over the connections, they all look good but I will go through them and try cleaning them as well as any visual grd wires. The battery tests fine, the voltage was a bit low from it running during the testing with no charging.. I'd really like to understand why it bench tests ok, the more I think about it the more it makes sense that a grd connection somewhere may be the culprit, even still shouldn't I get 14+ volts out of one of the alt pins during a running engine test?

 

You have the infamous 2G alternator?
I would suggest changing the charging plug pigtail as outlined in Ford TSB 96214.
"At any time the charging system or battery is serviced"


"Ford TSB 96214, applies to F150 through F350, model years 1986 through 1994
(The TSB also applies to numerous other car and truck models)

ISSUE:
When a generator fails, there are a few failure modes that may cause heat to be produced at the wiring harness-to-generator connector. This excess heat may damage the female terminals on the wiring harness, resulting in increased resistance. The increased resistance produces more heat. When the generator is replaced, the resistance produced by a damaged connector may damage the new generator and could result in a repeat repair, including installation of another generator. High resistance (caused by a damaged connector) will not go away until the damaged connector is replaced.

ACTION:
Visually inspect the harness-to-generator connector for damage (heat, corrosion, distortion and cracking) before installing a new generator. Install the Generator Wiring Harness Connector Kit (E5AZ-14305-AA) if the harness-to-generator connector is damaged.

The Generator Wiring Harness Connector Kit (E5AZ-14305-AA) contains the following:

^ One (1) Red Wire Butt Connector
^ Two (2) Yellow Wire Butt Connectors
^ One (1) Wire Connector Assembly
^ One (1) Instruction Sheet (I.S. 6849) "


These pigtails can be found at almost any parts store.
Here are a few examples...

Borg-Warner PT-780
Standard Motor Products S-542
Power Plug 4628011
KEM Parts 350-220
Pico 5711
Dorman 85123
Motormite 08622
NAPA VRA400

 

Interesting, I will look into that. Thanks!!!

 

The other thing that could be causing a no output condition is if the lightgreen/red "exciter" wire is not telling the alternator to turn on.

Does your battery light come on when you turn the key to run, but before you start the engine?

 

Yes the engine light comes on with the key on run before starting

 

No. The Check Engine Light is NOT the Battery Light. The battery light has a red battery that illuminates. If this doesn't come on, the alternator isn't turning on via the green "Excitor" wire Jim was referring to.

It starts at the Alternator wiring pigtail, and goes to meet the Red/Green wire at the cluster, crossing over at the bulb position.

It goes: Alternator>Green Wire w/ Red Stripe>Battery Light Bulb>Red/Green power wire to the ignition switch.
You stole the words right outta my mouth Jim.

Another note. You can remove the bulb if faulty and cross it over via a piece of wire (Not recommended, but for short testing periods it works) to see if that's the issue.

 

I'm not sure about Matt's truck but I know my cluster has a resistor across the charging warning lamp trace or across the bulb holder itself, just so that the alternator won't fail to charge simply because the lamp or the fuse burns out.

That said, I would check for power at the green/red wire of the regulator plug with the key in run.
If there's nothing then it won't charge.

I'd still change the charging pigtail and put dielectric grease in the new plug to prevent corrosion.
(I hate those things...)

 

I miss spoke, the battery light does come on with KOEO

 

OK, Key in start postiion and the plug unplugged from the regulator I have battery voltage at the yellow and grn/red wires. Plugged in they each have just about 3 volts. With the engine running I have less than that.

 

This sounds to me like the shop that tested this only tested the alternator output versus the regulator output.

For the rest of you...does that sound "stupid"?

Maybe a relay issue?

At the same time...I have to wonder about the harness issue mentioned above. I have seen cables & harnesses that "looked" OK on the terminal ends, but if you sliced the cover you would see massive corossion

If you have a ohm meter I would be checking continuity between various wires. I know that sounds "old school"...but it's the only way to tell if a wire has corroded past it's usefullness.

JMHO

 

You've diagnosed the problem. Something is wrong with the Yellow/White wire. It should read what ever the battery voltage is all the time ignition On or Off.

If you disconnect it from the alternator regulator the Yellow/White wire should still read battery voltage.

The Yellow/White wire is connected to the same electrical point as the Black/Orange wires.
Both colored wires receive 12 volts from the battery positive terminal via a fusible link.

If the Yellow/White wire reads 3 volts are you saying the voltage on the Black/Orange wires is also 3 volts?