BigBlue1124

Attn: Steve83

Two part question with background after to give you context.

Does a 130 amp alternator work without any modifications when replacing a 95 amp alternator in a 1995 F150 5.0?

Why does my battery not charge when both battery and alternator have tested to be in good working order?

I have a 1995 f150 5.0 and the alternator went bad. (Tested with multimeter and bench tested at parts store to verify it no longer works) I decided to replace it with a 130 amp alternator that would normally be fitted to an E250. After researching the forums most people said this larger alt would work fine with my 5.0 although some suggested larger power wire and “mega fuse”. I left the wiring alone and after testing battery and alternator and verifying all connections between the two are clean and not damaged my battery will not charge.

Does the alternator to battery wire need to be upgraded?
Any suggestions would be helpful thanks!

BLDTruth

The alternator charging cable comes off the starter relay located on the fender - there is a fusible link, and then the cable that turns the alternator on originates from the other side of the fusible link. It's hard to explain, here is a diagram - ignore the red, its my paint scribble and I had to steal this diagram from one of my other threads. The 12 gauge fusible link is located almost directly after the fender relay on the alternator harness, then on the other side of that fusible link is the BK/O charging cable and the Y/W wire which is responsible for turning on the alternator. If the fusible link is damaged, you will get no charging. If there is anything wrong with the Y/W wire that originates at the fusible link and terminates on the alternator plug, it will not turn on. If you run a jumper wire from the Y/W wire on C154 to the terminal on C153 and it turns on, you know it is the Y/W wire that is damaged. If it still doesn't work then you may have a problem with that fusible link, which would prevent any charging at all.

There is no need to upgrade the factory alternator wiring with the 130A alternator - but if that fusible link is blown then it might be a good excuse to. I run a 4 gauge wire direct from the battery with an inline 8 gauge fusible link. Seems to work fine as long as you make sure all of the factory wiring to turn it on and off still works. I had to cut the Y/W wire and run it directly to the alternator charge post (C153), and I had to pull the LG/R wire out of the factory harness and reroute it to C139.

BigBlue1124

After replacing the fusible link my battery is only receiving 12.3V when running. I have trouble shot every ground connection and all seem to be fine. I’m down to the yellow wire but a bit confused on how to diagnose it.

Do do I just take the spliced end of the yellow where it joins the black wire and fusible link and attatch it to the B+ terminal on the alternator?

Thanks for for the help

BLDTruth

Yep - that would identify/eliminate the Y/W wire as the problem. Before you go cutting things, make sure the White/Black wire is also in good shape - its the one that runs from the 3 pin connector to the tiny 1 pin connector. That wire and that single pin connector get damaged a lot more than the Yellow wire.

BigBlue1124

Update:

Replaced the 3 pin plug that connects to the alt and tried jumping the yellow wire directly to the battery. No luck, still only getting 12.3 V.

I can’t think of anything else to diagnose. Any other suggestions? Thanks

BigBlue1124

Got a 3 pin plug And all new wiring. What exactly does the green wire do into the round connector? Haven’t diagnosed that yet other than resistance, which it had.

Steve83

This diagram's caption explains what each wire does:


(phone app link)

BTW
I don't like being called out in a thread. As you see, I'm not the only person who can help you, and it's not my job. If you want help, just post - anyone who wants to help will. Asking for one person discourages all the others who might be able to help (possibly better than the person you name).

BigBlue1124

Thanks Steve 83. Didn’t mean to call you out. I have gotten lots of good info from you and BLD truth in the past and I know your both very valid sources. Also we live by your quote when fixing things in my house “stop guessing and start diagnosing”.

As as far as this alternator goes I’m going to try grounding the voltage regulator to see what it can put out next. Hopefully I make a break through soon.

Thanks again for all the help

BigBlue1124

After grounding the “ground to test” from the alternator’s voltage regulator to the - on the battery it shot right up to 17 volts.

So my question now, is the voltage regulator bad? (I think not because it’s has been bench tested by two different parts stores and passed)

Or is the green indicator wire bad and not telling my voltage regulator to produce the 14 volts it needs to?

Where does the green indicator wire go to and is it controlled by a fuse maybe? It does have a plug that it connects to off the harness but all connections seem to be fine

Again, thanks for the advice

Steve83

That proves the alternator is OK, but it says nothing about the regulator.Parts store employees are not technicians. So their tests prove nothing.You tell us. What's its voltage at the regulator connector with the key in RUN?It doesn't tell the VR what voltage to produce. You need to re-read that caption more carefully. A few times, if necessary.