Charging issue - electrical folks please read

[1fast4]

So I picked up an 88 F150 w/ a 302 in it.

New battery
Alt checked good

Won't charge battery
Will run and idle fine when jumped and connected to another vehicle.
Soon as you disconnect, it starts to lose voltage pretty quickly.

Any suggestions on where to start and what to look for are greatly appreciated.

[TexasT]

What checked the alternator and determined it is good?
Sounds like the alternator isn't getting voltage back to it to excite the charging. Where are you checking the voltage? Is it putting out 12-14v at the back of the alternator with it hooked to other vehicle?

Does the battery pass a load test?
New parts do not equal good parts every time.

I think I'd swap in another alternator if you are swapping parts.

[1fast4]

I took the alt to O'Reilly's and had them check it. It passed several times.
Unfortunately the truck isn't at my house so I can't quickly check anything.
And I forgot my damn volt meter when I went there a little while ago.
Only way I have to check voltage is the dash gauge and watching it drop as it idles and then dies.

What I am looking for is any suggestions and what and where to look/trace when I do have time to go mess with it.

Thanks in advance for any and all advice/info received in this post!!!!

[TexasT]

Well, if the alt is spinning, power should be at the post on the rear of the alt. Sounds like it is when on the test stand so this leads me to believe there is a problem between the alt and bat. Fusable link? A continuity test on the wiring might tell something. I wish I could be more specific but I never worked on an 88 f150. Chasing the wiring and looking for insulation chafed or cut and shorting. Bring the meter next time.

[1fast4]

Thanks.

Will most definately have meter next time.

[G..]

If the batt light on dash does not illuminate when key is turned to on position the alt will not charge. Look when you go to start it and all the warning lights come on and verify you see a batt icon.

[DON SVO]

You say good battery and good alternator, but the car discharges pretty quick and dies? Sounds like you might need a better body and engine ground. It's running fine when jumped, so try jumping it again and only disconnecting the positive cable from both cars. See if it's running well using another vehicles grounding source.

[1fast4]

I will check grounds and the dash light.
The dash light is not on when connected to another vehicle but does become dimly lit when it's running under its own power. The light also either gets slightly brighter or dimmer as I throttle it.
Hopefully will have time after work tomorrow to go mess with it.

Thanks again for any and all suggestions!!!!

[Binky]

Had an issue similar on my 98. Fuse for the voltage regulator had blown and the alternator wouldnt charge the battery.

[1fast4]

Had an issue similar on my 98. Fuse for the voltage regulator had blown and the alternator wouldnt charge the battery.

I hope it's an easy issue like this. I HATE tracing electrical issues!!!

[1fast4]

Meter hooked up while running and jumped 13.2 at the battery & starter solenoid.
Disconnect negative from jumper and voltage drops to 12.xxx and slowly drops.
Disconnect positive from jumper and voltage drops

Have to go to work now so will look at the link able fuses next time.

[DON SVO]

Meter hooked up while running and jumped 13.2 at the battery & starter solenoid.
Disconnect negative from jumper and voltage drops to 12.xxx and slowly drops.
Disconnect positive from jumper and voltage drops

Have to go to work now so will look at the link able fuses next time.

Use cables and jump it from a running car.

[1fast4]

Use cables and jump it from a running car.

I was

[DON SVO]

I was

I read that wrong and it seemed at though you said jumper box. Sorry.

Pull the negative cable from the battery and connect the voltmeter and check it in Ohms.

[1fast4]

Ok. Will do next time.

Wasn't feeling very Zinish this morning

How many chants should it take?