I'm looking into purchasing a manual 1990 F250 truck with a 7.3L diesel engine that's been stored inside. Only 22,000 miles on it so far and has barely been used since it was bought in 1990. Frame and body are in great shape, next to no rust. Alternator was replaced about 5 years ago; the dual batteries are older but road tested fine and will charge up to 14 volts after running a bit (the vehicle has been sitting for some time).

The catch is the pesky battery light that remains on, despite the batteries holding their charge. I'd like to figure out if it's just a bad connection or something behind the dashboard before I spring to take it to a Ford dealer to run diagnostics. I don't want to be taken advantage of at the dealership as I'm a mid-20's female just looking for a steady truck to pull my horse trailer.

Any thoughts? Thanks!

 

Keep in mind these trucks only had a 5 digit odometer. See if you can get documentation proving that it's 22,000 miles and not 122,000 or 422,000.

The battery light is connected through the regulator of the alternator, and turns the alternator on. If the battery light stays on, there's generally a fault inside the alternator somewhere. Could be the regulator, or another internal problem.

 

Thanks Ian, I appreciate your input.

Fortunately I have info verifying it's just at 22k and not more.

 

Is the alternator still externally regulated? The light on the dash works by sensing there power on both sides so all is good, when no power it lights. If you voltage regulator is on fendor check to make sure you have power with key on to I terminal.

 

i would not take it to a dealer, that truck is probably older than all the "techs" in the service department.. if it is charging properly, i would just remove the bulb out of the dash and go by the voltmeter in the instrument cluster.

 

Removing the bulb disables the charging system on some trucks; not sure if that includes the OP's year. It also obviously removes an important warning system that can be made operational with the right repair.

 

Correct my truck won't charge with warning light gone. Which is a problem because the printed circuit is wore out

 

i agree.don't take it to a stealership.find yourself a good local mechanic/shop with a good reputation around town.take it to him and tell him,the light is staying on and that you want the alternator upgraded to a 3g.
he'll know what to do.your idi engines charging system will then be much more dependable.
the cost will probably be cheaper than ford just fixing the light lol!

 

i would never modify a "new" trucks electrical system to "upgrade" something that is working fine.

there is nothing wrong with the charging system except for the light being on. and even then there is nothing wrong with the current alternator and regulator to warrant modifying the electrical system

 

It's not working fine.

The battery light energizes the regulator, and the regulator turns the light off once the alternator is generating. Something is wrong with the regulator or alternator that's keeping the light on.

Upgrading to the 3G alternator is a far more reasonable option than your absolutely inane suggestion to just pull the light out.

 

a system that charges the batteries at 14 volts, and the batteries never go dead in my book is a working system that just happens to have a stupid idiot light on.
by eliminating the light bulb you still feed power to the circuit, you just use the gauge in the dash to see whether it is charging or not.
the 510 ohm resister in parallel with the bulb should still energize the regulator, which it apparently is because the alternator is putting out 14 volts when the engine is running, like it should. .

 

It's not a working system. The regulator or alternator is faulty in some manner. The light should NOT be on. Period. The regulator is not properly drawing power from the alternator output, and is relying on the bulb for some or all of the field power.