Charging issue help needed
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Elder User
Joined: Apr 2005
Posts: 533
Likes: 2
From: Lindenwold, NJ
Charging issue help needed
95 F150 2wd with a carbed 460 swaped into it. Has the stock serpentine brackets and alternator set up from a mid 90s F250 and the stock alternator harness. New battery, rebuilt alternator that was checked at 2 Autozones and 1 Advance auto. Tried a known working alt harness from another truck but the battery light is still on and it shows very low voltage. I have a multimeter and it seems to be getting power with the key from the green/red wire all the way to the alt but it only puts out the same voltage as the battery which is 11.5v. Im not the best with trouble shooting so tell me what to check and how to check it please so I can get this thing back on the road 
And I did search but couldn't come up with a solution. It worked fine before than intermittently had issues and now its completely undriveable.
And I did search but couldn't come up with a solution. It worked fine before than intermittently had issues and now its completely undriveable.
Fleet Owner
Joined: Oct 2005
Posts: 20,789
Likes: 1,753
From: Kentucky
Please verify which alternator you now have in the truck a 2G or 3g. Your 1995 most likely had a 3G. The older 1990 engine came with the POS 2G, aka fire hazard. If you have the 2G in there you are missing some wiring to make it work. Do yourself a favor, if you are running a 2G, get a 3G and be done with it.
Fleet Owner
Joined: Oct 2005
Posts: 20,789
Likes: 1,753
From: Kentucky
Okay, now I understand your setup. You already verified the green/red wires is hot with the key on.
Ryan @ oldfuelinjection.com has some good info on wiring up 3G alternators. Here is a link to the info for many different versions: Fuel Injection Technical Library » Alternator Files
This photo here might help you out too:
There should be an inline fuse for the charge wire to the battery, perhaps the fuse is blown?
Ryan @ oldfuelinjection.com has some good info on wiring up 3G alternators. Here is a link to the info for many different versions: Fuel Injection Technical Library » Alternator Files
This photo here might help you out too:
There should be an inline fuse for the charge wire to the battery, perhaps the fuse is blown?
Thread Starter
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Elder User
Joined: Apr 2005
Posts: 533
Likes: 2
From: Lindenwold, NJ
OK I checked all the wires in the harness for continuity with a multimeter and all tested good. Fusible links checked good. Checked all fuses in both the under hood and under dash fuse boxes. Shows 11.6v from the green/red wire from the harness to the alternator with the key on. Took it to the parts store and had it checked while I watched and tested it myself while on the machine with my multimeter and it put out 15.1v. Back on truck 11.6-11.7v. Than I ran i jumper wire straight from the battery to the energizing post on the alt and still 11.6. Im completely stumped.
The battery light does not come on with the key or while its running. I have no clue if that is related.
The battery light does not come on with the key or while its running. I have no clue if that is related.
Posting Guru
Joined: Jan 2002
Posts: 1,346
Likes: 8
From: Baltimore
If the posted diagram is correct, you should measure 12 volts at all times on
the Yellow/White wire.
The dash charge indicator should light when you turn the ignition on.
The voltage regulator provides the ground path to turn the bulb on.
Since you swapped the engines, make sure you have a good ground
from the engine to the negative battery cable because the engine
is the ground path for the alternator.
the Yellow/White wire.
The dash charge indicator should light when you turn the ignition on.
The voltage regulator provides the ground path to turn the bulb on.
Since you swapped the engines, make sure you have a good ground
from the engine to the negative battery cable because the engine
is the ground path for the alternator.
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pedant
Joined: Jan 2008
Posts: 23,576
Likes: 40
From: EXTREME southwest CT
Not really.
The yellow/white wire (alternator output) should be ~14.3V engine running.
You can't 'charge' a 12V battery with 12V.
A 12V battery should show over 13.5V engine on, and about 12.5V at rest.
Yes, the charge indicator bulb provides current to excite the alternator.
That is why the bulb lights, voltage differential across the filament.
But there should be a resistor in parallel to the bulb (on the foil circuit board) to provide current if the bulb burns out.
The yellow/white wire (alternator output) should be ~14.3V engine running.
You can't 'charge' a 12V battery with 12V.
A 12V battery should show over 13.5V engine on, and about 12.5V at rest.
Yes, the charge indicator bulb provides current to excite the alternator.
That is why the bulb lights, voltage differential across the filament.
But there should be a resistor in parallel to the bulb (on the foil circuit board) to provide current if the bulb burns out.
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Post Fiend
Joined: Apr 2004
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From: Lafayette, IN
Jason
Posting Guru
Joined: Jan 2002
Posts: 1,346
Likes: 8
From: Baltimore
The Yellow/White wire is the sense voltage for the regulator. If there is no
sense voltage to the alternator regulator, what will be the voltage be at
the alternator battery terminal post?
The original poster did not mention what voltage is on the Yellow/White wire
at the regulator plug end.
Of course it should always read what ever the battery voltage is since it's
connected to the positive terminal of the battery if it's wired like the
posted diagram.
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Elder User
Joined: Apr 2005
Posts: 533
Likes: 2
From: Lindenwold, NJ
Ok I finally figured this out. After swapping batteries from another running truck, swapping alt harnesses from another running truck and finally having the alt converted to be self energizing (1 wire) with no luck it ended up being a ground issue like F150xlt said. It has a good ground from the battery to the frame, block and fender and a ground from the firewall to the intake bolt but it still wasn't grounding the alt. Had it running with the multimeter and ran a wire from the neg to the alt body and boom 14 volts 
So I ran a wire from the alt body to the block and all is good. It should ground through the bracket but my theory is the bracket is powdercoated and possibly not grounding like it should. Put 100 or so miles on it with zero issues. Thanks for the help. Sucks it took so damn long haha
So I ran a wire from the alt body to the block and all is good. It should ground through the bracket but my theory is the bracket is powdercoated and possibly not grounding like it should. Put 100 or so miles on it with zero issues. Thanks for the help. Sucks it took so damn long haha
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