'76 electrical issue(s)

[poptop tom]

I have two problems!!

For those that didnt follow the rebuild thread.

I finished the final portion of my resto last fall with an engine rebuild. Installed the rebuilt 2.0, broke it in, and drove to Florida three days later. (In fact, Colin stopped by to help me get the engine in and fired up and the 20 minute break-in procedure.) Made it there and back with only two issues - the first was a bad ignition switch. The second was me running out of gas!

Anyhow, when I got the rebuild going, my alternator light would not shut off at all. Always glowing a solid red color, even when driving it. I had my 70 amp alternator rebuilt locally, along with my starter before installing the engine. Colin helped wire the starter up. And the alternator had a nice condition harness. In fact, I liked it better than the new replacement I purchased from Jim Thompson of Sherwood Auto.

So this is problem 1. Alt light always on. I have no clue, at this point, whether the alternator is charging.

Problem 2 is that I have something else draining my battery while it sits. With the ground cable off and the battery charged, the battery sits around 12.8 v. As soon as I hook the negative cable up, it drops the voltage to 12.6.

So I removed the fuses for the stereo and the clock. No change.
I then removed the fuse for the idiot lights. No change.
I then removed all fuses. And when I hook the neg cable up, it sparks a little bit (when moving the cable across the post), and continues to draw the battery down.

I have new ground straps at the tranny and the battery. New pos cable from battery to alt.

Any ideas?

I'd imagine I need to fix issue #2 before I can get to issue #1. Unless they are tied together.
Also. This issue was there from the get-go when Colin and I first put power to the old girl.

[dtrumbo]

You're on the right track by removing fuses to isolate the problem. Since you haven't found the problem yet, we have to dig further. The positive battery cable goes directly to the starter. At that point (terminal 30) there should be the black wire that comes from the battery, a red wire that goes to a fuse holder very near your heater blower motor in your engine compartment (if it's still there), another red wire that goes to your alternator and finally a red & white wire that goes up front to your fuse box. One at a time, disconnect the reds and red/white and see if your sparky-spark when connecting the negative battery cable goes away. Once it does, you've found the branch circuit that contains your current draw. From there you can figure out what actual component is the problem.

My money is on the alternator.

Let us know what you find.

[Amskeptic]

This issue was there from the get-go when Colin and I first put power to the old girl.

Disconnect the negative terminal to the battery.
Remove the plug at the voltage regulator.
Test for drain.
Report here.

If still a drain, remove the alt warning lamp.
Test for drain.
Report here.

If still a drain, remove the alternator main wire from the starter solenoid terminal.
Test for drain.
Report here.

If still a drain, shoot it.
Colin

[poptop tom]

This issue was there from the get-go when Colin and I first put power to the old girl.

Disconnect the negative terminal to the battery.
Remove the plug at the voltage regulator.
Test for drain.
Report here.

If still a drain, remove the alt warning lamp.
Test for drain.
Report here.

If still a drain, remove the alternator main wire from the starter solenoid terminal.
Test for drain.
Report here.

If still a drain, shoot it.
Colin

Removed plug at VR and no draw on the battery! That's good news!(I hope)

Now what? I'm sure its not as easy as simply replacing the voltage regulator. And I was correct. Two different VR's yield the same results - a draw.

I'll hold off on shooting her! I'm a poor shoot anyhow.

[Amskeptic]

Disconnect the negative terminal to the battery.
Remove the plug at the voltage regulator.
Test for drain.
Report here.

Removed plug at VR and no draw on the battery! That's good news!(I hope)

You need an alternator! Excitor diodes leaking to ground.
Colin

[poptop tom]

Can they be replaced, instead of replacing the whole alternator?

I've already had the brushes and two bearings replaced on the unit. And I'd like to hang onto the 70 amp. Especially since I have the correct harness, boot, etc. for it.

[Amskeptic]

Can they be replaced, instead of replacing the whole alternator?

I've already had the brushes and two bearings replaced on the unit. And I'd like to hang onto the 70 amp. Especially since I have the correct harness, boot, etc. for it.

If they are available and good work practice is observed, why not?
Colin

[dingo]

yes, the diodes can absolutely be replaced...depending on how dexterous/patient you are with soldering iron and long-nosed pliers. You can easily isolate which one is bad, by using a multimeter on ohms...should show resistance in one direction (500 ohms or thereabouts? ) and NO continuity in the other direction. The bad one will show continuity/resistance...

[poptop tom]

Thanks for that info Colin and dingo! I asked because it said on ratwell's site that the diodes are tough to find in the USA for the 70 amp since there were so few produced.
The part # for the diode pack comes up NLA supposedly. And after a quick search of my own, I came up empty.

Another question!

Does the blue wire that runs from the VR to the alt. light at the dash run a continual run? Or does it go elsewhere before completing that circuit?
Does the blue wire run out of the same harness, into the engine compartment, and up to the VR to make that connection?

Thanks again for the help!

[dingo]

if the need arises, im sure diodes can be found...i have a bin full of bosch alt stuff from volvo , saab, benz...im sure those diodes would easily cope with 70A...Bosch stuff from that era is very similar design,components

[Amskeptic]

blue wire that runs from the VR to the alt. light at the dash continual?

Yep. Sometimes is branched to also energize the heater blower relay coil on earlier Type 4 buses.
Colin

[poptop tom]

blue wire that runs from the VR to the alt. light at the dash continual?

Yep. Sometimes is branched to also energize the heater blower relay coil on earlier Type 4 buses.
Colin

I hate asking, but does anyone have a clear picture of where the blue wire exits the harness and heads up to
the VR? My blue wire is definitely NOT wired up in that location. So I unplugged the alt light. Ran a wire from the alt light connection all the way back to the blue wire at the alt harness plug of the VR.

And I still have a draw on the battery.
I have not had a chance to fire up the bus to see if that alt light is now continually on, or not, as it was before.

if the need arises, im sure diodes can be found...i have a bin full of bosch alt stuff from volvo , saab, benz...im sure those diodes would easily cope with 70A...Bosch stuff from that era is very similar design,components

That's a relief. My local builder can hopefully find them. Especially since he didnt apparently check the diodes when doing the work on it initially. Tomorrow I will get the bus running and see if the alt light remains on and if the alternator is charging when running.

[dingo]

my blue wire pops out of the harness close to the end by the VR. Blue wire is connected to D+ red wire i.e. output of D+(red) is what dash light is seeing.

[Amskeptic]

my blue wire pops out of the harness close to the end by the VR. Blue wire is connected to D+ red wire i.e. output of D+(red) is what dash light is seeing.

All bus alternator blue wires are connected to D+ . All alternator buses with alternator-run heater blowers ALSO have a wire on that run that goes to the heater relay at the ceiling.
Colin

[poptop tom]

Apologies for my denseness. But now I'm lost.

What is the red wire being mentioned?

I have a blue wire hanging 5" down loosely from the plug that goes into the VR. I have no blue wire sticking up out of the harness where I assume I should.

I have a blue wire behind the dash that goes to the bulb of the alt light. Where this wire goes I have no clue.
I assumed that it ran directly from the alt light to where it needs to be hooked together with the blue wire coming out of the VR.
Which is why I ran a wire direct from the alt light to the VR as a test. Is that wrong?
Sorry for my confusion and thanks for the help.