Battery Issue -- Not the Battery or Alternator

[ksteak1]

The other day, the AMP/battery discharge light came on in my 1987 LX 5.0 (~115K). I drove it for a while, but the battery gauge got lower and lower. The car was dead by the time I got home.

Took the battery to Autozone to be tested -- they said it was bad. Bought a new battery. Nothing changed (gauge in the red, AMP light on).

Took the alternator to Autozone to be tested -- they said it was bad. Bought a new alternator. Nothing changed (gauge in the red, AMP light on).

(Starting to wonder if Autozone just wants me to buy stuff!!!)

Anyway, what should I check next? It looks like my car is running just on the juice in the battery which will no doubt not last long. It doesn't appear to be charging correctly, despite the new alternator.

Do 87's have an external voltage regulator or is it inside the alternator like on newer Mustangs?

Any suggestions on what to check??? THANKS!

 

[jrichker]

No alternator output 86-93 model cars.

If a battery is too low, it will not supply enough power for the alternator field windings to generate the 13.8-14.2 volts needed to charge the battery. The best thing you can do is have the alternator bench tested before you take it out of the store. DOA electrical parts are not uncommon. Have the battery charged up to 12.8-13.2 volts before expecting it to provide sufficient power to operate the alternator.

If the alternator checks good, look closely at the power connector plug (2 black/orange wires) for the stock alternator. They tend to overhead and burn up. Every replacement alternator should include a pigtail replacement plug.

Next check the black/orange power plug for voltage at the alternator end. With the engine off, disconnect it at the alternator. Ground one probe of the voltmeter to the battery negative terminal and put the other probe on the metal contacts for the black/orange wires. You should see battery voltage, whatever that may be. No voltage and the fuse link that protects the wiring has burned up.

The secondary power ground is between the back of the intake manifold and the driver's side firewall. It is often missing or loose. It supplies ground for the alternator, A/C compressor clutch and other electrical accessories such as the gauges.

 

[ksteak1]

Awesome buddy! Thanks! I will check that stuff out tonight and get back to ya!

 

[Black Sun 5.0]

Yeah, check your grounds and maybe clean up the contacts. I had something very similar going on with my car that I just got back from the body shop. All the grounds were connected to freshly painted metal and the battery was not being charged properly. Cleaned everything up, battery is now charging. Now I just have to figure out that no start when hot issue..........

 

[ksteak1]

I replaced the alternator connector (the wider of the two that plug into the alternator)... still no change. I could not find a replacement for the smaller half-circle plug at my auto parts store...

I looked between the intake manifold and the driver's side and found the ground in the picture below. Is this the right one? It's sorta a flat rope-looking wire. It looks fine... tight and all... (or am I looking at the wrong spot?)

Probably unrelated, but I also found this plug on the driver's side... not plugged into anything and nothing nearby into which to plug! Any idea what this is for?

Any other electrical grounds to check? Also, can I find the smaller alternator plug anywhere? Will try the Ford dealership today.

 

[ksteak1]

Found the smaller alternator clip on Ebay over the weekend... will hopefully arrive today. So far I've replaced the battery, alternator, and larger alternator connector... and charged the battery... and still it's discharging.

Still open to advice!

 

[89 Saleen#455]

Grab yourself a volt meter and test both the battery and the alternator. First test the battery with the car off. You should see 12+ volts. If you're not seeing 12+ volts, then 1 of 2 things is happening: 1) The alternator is not charging the battery or 2) The alternator IS charging the battery, but something (radio, alarm, etc.) is draining the battery when the car is shut off. Next test the voltage at the battery with the car running. You should be seeing 13.8 - 14.5 volts at idle. If your seeing anything less then 13 volts at idle, then your alternator needs to be replaced.

Test those components and let us know your findings so we can start narrowing down your problem.

 

[jrichker]

I replaced the alternator connector (the wider of the two that plug into the alternator)... still no change. I could not find a replacement for the smaller half-circle plug at my auto parts store...

I looked between the intake manifold and the driver's side and found the ground in the picture below. Is this the right one? It's sorta a flat rope-looking wire. It looks fine... tight and all... (or am I looking at the wrong spot?)

Probably unrelated, but I also found this plug on the driver's side... not plugged into anything and nothing nearby into which to plug! Any idea what this is for?

Any other electrical grounds to check? Also, can I find the smaller alternator plug anywhere? Will try the Ford dealership today.

The flat looking braided cable is the secondary power ground.

The loose connector is the computer diagnostic connector.

The small alternator connector does not need to be replaced. It is not the one that overheats and charcoals. The big connectot is the one that overheats.

 

[Mustang5oh88]

any work done to it recently? i had this happen to me and it was because the rear crash bumper was not bolted up all the way....sounds stupid i know....it only took me 3 weeks to figure it out.....

 

[ksteak1]

BOOOOYAAA!!! Figured it out last night!

Turns out there was a green wire connected to my starter solenoid that had melted/broke... didn't notice it before. Connected it back up and PRESTO... problem solved!

Thanks for all your help! I did measure voltage before I got it fixed (12.8 with car off and 12.5 with car running -- so the alternator definitely wasn't charging...)

One stupid wire... and I unnecessarily bought a new battery, alternator, and both alternator connectors... hahaha I suck. Oh well, I guess it can't hurt to have new stuff in the car.