1993 Charging System

[onerchprk]

I have a 93 Aerostar 3.0 i am having trouble with.The van has a good alternator and a good battery but still wont charge.The question is what should i check?The owners manual states that the fusible link by the starter relay could be bad?If so does anyone have a picture of what i am looking for or does someone know how to tell if a fusible link is bad?Also could the starter cause a charging problem?Please any help will be apreciated.Thanks

[Selectron]

I'm not familiar with the Aerostar but I can see the wiring diagram in the Repair Info section at the Autozone website. The diagrams aren't always fully accurate, but this is what they're showing as the charging system for the '93 - if the first link doesn't work then try the second:

Link 1
Link 2

If the diagram is accurate then there are three fusible links associated with the alternator.

You'll see that one runs from the battery to the alternator's 'B+' output terminal. With the engine and ignition switched OFF, check for 12V at the B+ terminal - it should be present at all times. If 12V is missing then the fusible link is open-circuit.

Another fusible link runs from the battery to the 'A' terminal - this feeds the alternator's field coils, and if it's missing then the alternator cannot produce any output. Again, that should be present at all times so check for 12V with the engine and ignition switched off, and again if 12V is missing then the fusible link is open-circuit.

The third fusible link runs from the ignition switch to the 'I' terminal, and this carries the signal to switch the alternator on, so if 12V is missing then the alternator won't be able to produce any output. However, that link also carries current to the starter solenoid, so if the starter cranks then the fusible link must be good, so no need to check it. The current which signals the alternator to switch on also flows via the ignition switch and then to the charge warning lamp on the dashboard - if the lamp illuminates when you switch the ignition on then that section of the ignition switch must also be good, and current must be reaching the alternator, so no further checks needed there either.

A fault in the starter circuit won't affect the charging system, but I do notice that the last fusible link which I mentioned, for the 'I' terminal, connects to the starter relay, so a bad connection there could result in no charging but if the charge warning lamp indicates then the connection should be ok.

Fusible links are just short sections of wire of a smaller gauge than the wires which they protect, spliced into that main wire. The short section of fusible link will be protected by special non-flammable insulation, and if it blows then it will overheat and you would expect to see heat damage in the form of blistering on that insulation.

The alternator's B+ output terminal is usually a large stud, with the wire secured by a nut, and it will be separate from the other alternator wires, which usually connect via plug and socket. I'm hoping the colours indicated on the wiring diagram will be accurate and you'll be able to identify the A and I terminals by the colours. Either a multimeter on its DC voltage range or a 12V test lamp will be fine for checking for the presence of 12V. Let me know if you don't follow any of that.

[onerchprk]

Thanks i will give it a try but i have a problem?I had the starter removed to check it before i read your reply.I put the starter back in just a bit ago but now when i hook up the battery the starter kicks in and cranks the engine.What could have happened?Could a bad starter relay cause the charging problem?Please help me out.

[Selectron]

No, the starter relay isn't involved in the charging circuit so it won't be causing the charging problem.

I assume the starter was able to crank the engine normally before you removed it. You didn't mention removing the starter relay so I assume that hasn't been disturbed. In that case, I think you've connected the starter motor incorrectly.

The starter motor will have three connections - there will two large threaded studs with heavy gauge wires connected, and then a smaller terminal with a correspondingly smaller wire. Is it possible that you have swapped the two heavy gauge wires around and connected them to the wrong terminals? That would cause the starter motor to crank as soon as you connect the battery.

[onerchprk]

I found out the culprit it was two wires touching at the start relay.I tested all the fusible links and they all had power.I am stumped.

[Selectron]

What's the history of the alternator which is now in the vehicle - is it the original or a rebuilt replacement or a new Ford replacement or what? Rebuilt alternators aren't always reliable - we often hear of a rebuilt being fitted but then it turns out to be faulty and it has to be replaced again, and then sometimes the second rebuilt will be also be faulty and it has to be replaced too.

Have you had the alternator tested? Some places can bench test them, off of the vehicle, so if you haven't already done that then I'd be considering that next. It's a fairly simple circuit - not much to go wrong with it, so if the fusible links and connections are good then it should be working.

[onerchprk]

This is a used one.Actually the 3rd one i have tried.I have had it tested at Autozone and it tested good.I must be missing something somewhere..

[Selectron]

I assume you're verifying a lack of output with a multimeter, in which case you'll have twelve-point-something volts at the battery prior to starting the engine, and then when the engine is running the voltage will steadily fall. If the alternator was working then you would have around 12.6V prior to starting the engine, and then with the engine running at idle speed it would rise to probably around 13.8V, settling at around 14.4 when the vehicle was running at road speed.

Sometimes a vehicle will have excessive current drain when it's switched off and parked, leading to a flat battery next morning and that can be misdiagnosed as a charging problem, but a voltage check at the battery before and after starting the engine will quickly tell you if the alternator is working.

I'm all out of ideas on this one and don't know what to suggest next, except maybe to check the wiring again.

[rhandwor]

I would take the alternator to a rebuild shop where they can check it properly.
I know on Chevrolet's the light bulb for the charge light is needed for the alternator to work. I've also had to change the ammeter to get them to work.
The field needs excited for an alternator to work. They make self exciters for boat alternators. Check all plugs on the back of the alternator.
http://www.nationsautoelectric.com/regulators.html