Replaced VR and then Alternator - still no charge

[DPDISXR4Ti]

'89 w/ 2.3 engine and without obvious cause, the battery charging light is illuminated. Verified no-charge condition at battery. Knowing it's most often the voltage regulator that fails, I first tried swapping that. No change. I tried re-freshing the contacts on both connectors and dabbed a bit of Kopr-Shield on each of the contact points. No change. I swapped in a new alternator. No change.

Thoughts?

 

[CamTheHedgehog]

Hmmmm... I would start by double checking the alternator with a multimeter, sometimes (parts house units especially) they are dead out of the box. Put positive on the main terminal, negative on the body of the alternator.

If it passes, then you need to start looking at wiring- the truck starts and runs I assume, so the main battery cable is not the issue- but most vehicles have a slightly thinner wire that branches off the main positive wire and travels to the alternator. I would check that, to make sure that there is no obvious break or damage to the wire. Also run a voltage drop (or resistance I suppose) test between the main battery positive terminal on the battery and the positive alternator terminal.

If the positive wire passes both of those tests, it is now most likely a ground issue. The alternator's body is the negative terminal, so it must make a good connection to the block. If that connection is good, then check between the engine block and the frame, often there has to be a ground strap between the two, as rubber engine mounts are insulating. Run the same resistance and voltage drop tests, essentially to make sure the alternator body is well connected (electrically) to the battery negative.

If none of that is the issue, then I am stumped.

 

[RonD]

+1 ^^^

Alternator has 3 wires you need to test
B+ is the stud/nut terminal on the back of the alternator
As said above use the alternators metal case as the ground for all tests
Key OFF
B+ should show Battery Volts, leave wire attached, exactly the same as battery volts
If not then a fuse or fusible link is bad
This is the Voltage OUT to Battery positive so has a fuse at battery end of wiring

Unplug the 2 or 3 wire connector on alternator
Test the Yellow/White wire, should also show Battery volts, exactly
If not a fuse in engine bay fuse box is blown
This is the Voltage regulator's Monitor wire, tells the VR the alternator's output voltage to vehicle, so when you turn on headlights, for example, it sees the voltage drop and increases alternator's output voltage

Test the Green/Red wire, should be 0 volts
Turn the key ON
Re-test greed/red wire should now be 12volts, can be slight less than battery volts
This is the battery light wire, also the ON/OFF switch for alternator/voltage regulator
If this wire was grounded in the harness or in the dash area then battery light would come on but no alternator

If there is a 3rd White jumper wire then make sure it is plugged into the single spade terminal in the back of alternator, it can go in above or below the terminal so no connection and no alternator voltage

If the 3 wires voltages test as OK, and no charging after start up then alternator is bad, period, new or not

 

[DPDISXR4Ti]

Thanks for the excellent and detailed diagnostic path. I need to take my own advise and do actual diags first rather than being a brainless parts swapper.

 

[DPDISXR4Ti]

Alternator has 3 wires you need to test
B+ is the stud/nut terminal on the back of the alternator

Just re-reading this and I realize you probably are thinking this is a 3G alternator. It's not - it's a 2G. If it was my truck (it's my neighbor's), I would upgrade to a 3G, but trying to keep this as close to stock as possible.

 

[RonD]

The wiring tests are the same

2G wiring: https://i664.photobucket.com/albums/vv8/honda53rider/2G-ALT_wiring_zpsmkjcif0n.gif

3G wiring: https://www.fullsizebronco.com/attachments/1700340592269-png.222663/

 

[DPDISXR4Ti]

2G wiring: https://i664.photobucket.com/albums/vv8/honda53rider/2G-ALT_wiring_zpsmkjcif0n.gif

Printed this out and wrote down some testing notes. I presume if the fuse had failed on the Grn/Red circuit that goes back through the instrument cluster, the battery light wouldn't even come on, yes? I'll check that fuse regardless, but just wanted to know if the fuse was really in play as the point of failure.

 

[RonD]

Correct, and it has no fuse in 1989

 

[DPDISXR4Ti]

I only had a few minutes to do some quick diags this morning before the rain picked up (truck is outside). I found ZERO voltage on the dual B+ circuits, as measured at the alternator connector. I then checked the mega circuit box and found that one of the 60A fuses had blown. I'll swap in a good one tomorrow and report back. Do we figure I found the problem?

 

[RonD]

I don't have a 1989 charging diagram but do have a 1990 one

If does show TWO 60amp fuses for B+ wires, fuses 3 and 7

 

[DPDISXR4Ti]

If does show TWO 60amp fuses for B+ wires, fuses 3 and 7

Thanks for the schematic. Yep, that's what I've got here on the '89. There were definitely two 60A fuses in there.

 

[DPDISXR4Ti]

Fixed! After verifying that fuse #7 was fine, I replaced the #3 fuse. All good and charging away now.

Thanks for all the help here.