diagnosing alternator or wiring

[RyanJustRyan]

1976 Bay window bus - moved 2.0 type 4 (79 engine) / trans /external regulator over from donor car. No idea if alternator was working in previous vehicle unfortunately.

Found the rat well advice - I'm new to using my multimeter but I think the idea is I stick the red in the prong and black to ground and report the readings.

Ignition off
Lamp off
D+ 0
Df 0
D- 0

Ignition on
Lamp on
D+ 4.3
Df 0
D- 0

Running
Lamp on
D+ 4.5
Df 0
D- 0

Fast idle doesn’t change anything

I see some harness hacks ... wondering if this is a wiring problem or an alternator problem ... should that black wire be merged there?

[RyanJustRyan]

and I got a text back from previous owner he said the alternator and regulator worked fine before.

So I'm assuming something wiring related at this point.

If anyone has guidance I'd appreciate it. Thanks.

[telford dorr]

TEST
----
- make up a short (6") jumper wire with a male blade terminal on either end.
- unplug regulator.
- plug jumper wire into regulator plug between D+ (red, blue wire) and Df (green wire).
- connect a voltmeter across battery.
- start engine. DO NOT REV!!!
- slowly increase speed while watching voltmeter. Do not let it exceed 14.4 volts.
- if voltage increases with engine speed, then the alternator and harness are good, regulator questionable. If not, remove alternator and check harness wires for continuity and shorts. If nothing found, suspect failed alternator.

What we are doing here is taking the regulator out of the charging circuit and running the alternator WIDE OPEN (unregulated). In this mode, voltage is only controlled by engine speed and, if allowed, can increase to damaging levels, so be careful!!!
_________________
'71 panel, now with FI
'Experience' is the ability to recognize a mistake when you're making it again - Franklin P. Jones
In theory, theory works in practice; in practice, it doesn't - William T. Harbaugh
When you're dead, you don't know you're dead. The pain is only felt by others.
Same thing happens when you're stupid. - Philippe Geluck
More VW electrical at http://telforddorr.com/ (available 9am to 9pm PST)

[RyanJustRyan]

Thank you telford dorr. Unregulated - getting 15.3 at idle. I didn't rev it up due to concerns that it seems high already.

I'm concerned that since you said don't let it exceed 14.4 - is the alternator generating too much voltage? Or does this suggest failed regulator?

thank you.

[mikedjames]

Some regulators need the case grounded to work rather than using the wiring from the alternator to provide a ground.
_________________
Ancient vehicles and vessels

1974 VW T2 : Devon Eurovette camper with 1641 DP T1 engine, Progressive carb, full flow oil cooler, EDIS crank timed ignition.
Engine 1: 40k miles (rocker shaft clip fell off), Engine 2: 30k miles (rebuild, dropped valve). Engine 3: a JK Preservation Parts "new" engine, aluminium case: 26k miles: new top end.
Gearbox rebuild 2021 by Bears.

1979 Westerly GK24 24 foot racer/cruiser yacht Forethought of Gosport.
1973 wooden Pacer sailing dinghy

[telford dorr]

Failed regulator (or ground, above).
_________________
'71 panel, now with FI
'Experience' is the ability to recognize a mistake when you're making it again - Franklin P. Jones
In theory, theory works in practice; in practice, it doesn't - William T. Harbaugh
When you're dead, you don't know you're dead. The pain is only felt by others.
Same thing happens when you're stupid. - Philippe Geluck
More VW electrical at http://telforddorr.com/ (available 9am to 9pm PST)

[RyanJustRyan]

[RyanJustRyan]

thanks for the assist, the new regulator resolved the charging issue.