Fox T-Bird/Cougar Forums

Yes, my Black is very jealous of the Red one.
The Black one blew the Alternator a few weeks back.
Now it will drain the battery sitting overnight.
I have tried different batteries so I know that is not the problem.
Right now, I'm thinking possibly starter or solenoid.
What do you think ?

Check after dark for any light from under hood, glove box or trunk.
Disconnect the negative battery cable. Connect a test light between the cable and the negative battery post.
If the test light lights, you have a power drain.
At the starter relay, disconnect the positive battery cable and all the wires from the battery cable post on the relay.
Touch the wires one at a time to the battery cable to see which one lights the light.

What year and engine do you have?

What year and engine do you have?

88 5.0 Original motor about 220 thousand miles.

I like your ideas !

You can also check across the fuses with the test light for a draw. Realize when you open the door the circuit the curtsey lights are on will draw current.

My loss on my Mustang was the starter. 

Here are some 88 Tbird/Cougar EVTM diagrams.
I highlighted the only fuses that should have power with the key off on the fuse panel diagram.
If any other fuses have power, you could be looking at an ignition switch problem.

Fuse test light probe points.

I had an aftermarket radio go bad and put a parasitic drain on the system but it wasn't over a night.

That's something like 12-30W to kill it overnight.

You can get more precise by putting a multimeter with a 10A fused setting inline with the negative battery cable. Start systematically disconnecting stuff and see when the draw stops.

Had not had much time to work on this.

Today I had the car running and the alternator was incredibility hot.

That one was good when I put it on the shelf 10 years ago  :smile:

The wires to the alternator were hot too.

Next chance I get, I'll put on another Alt that I have and see the difference.  

Bad diodes in the alternator can drain a battery overnight. That was my first guess but I thought you put a known good one on there.

Thanks, I put a different Alternator on today.

I have many on my shelf, all worked well when they were removed but at least one has been there for 20 years.

We will see what happens tomorrow.

Now I have a new mystery.

The wire harness on my car has the 3rd wire disconnected between the two plugs.

My project car is the same.

This is a wire harness from a parts car with the 3rd wire connected.



Is this wire necessary ?

Think I answered my own question through google.

"What is the small wire on an alternator?
The small wire that loops from one part of the alternator to another is the sensing wire, responsible for determining the output of the alternator. It’s an important piece of the wiring system and makes sure the electrical systems and the engine itself operate correctly."

None of those stock (2G) alts are worth a red .

I had a fire on an '89 Tbird from the connector melting, basically the voltage reg went bad and things got....hot..

Anywho....not really relevant, BUT, if you need more amps, then a 3G and upgraded wiring/connectors may be the thing. Write up on coolcats tells how, and what ya need, as well as what to find em on, if you;re the sort that likes getting your hands dirty twice ;)

The "third wire" is from the S (Stator) alternator output to the S (Switch) input on the regulator.
This causes the regulator to Switch Off the Alt/Batt/Idiot light when the alternator has output.
Cars with an ammeter  don't use this wire.

That makes perfect sense as both these cars are 88 XR-7s with gauges and the parts car was a LS with the digital dash.

Thanks !