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240 (1993) Charging Problem


New member
Mar 30, 2004
Hi all,

A few months ago the Battery Charging Indicator light started glowing very faintly (can't see it in daylight) when running. The light glows full-bright with the key on and engine not running. I figured the faint glow was something I could ignore for a while, because the battery (about a year old) did not discharge notably. Over the period of a couple of weeks recently though, the battery discharges after about 8 hours of running and now I have to do something about it.

The car has nearly 400k miles, so I figured alternator brushes were called for. Checked them, they needed replacing but none were available locally so I bought a rebuilt alternator and installed it. Same exact signs and symptoms. I put a voltmeter on the battery and got a reading of about 12.8 V when running and 12.0 V when not.

Several years ago the alternator wire chaffed through at the alternator bracket and melted the harness, including both the fat and the skinny red wires from the alternator. I used what was on hand (not horribly funky, but not ideal) to repair it and it'd been fine. Thinking maybe that fix was failing and just dinking around w/o a wiring diagram, I temporarily connected a wire from the alternator terminal for the skinny red wire straight to the positive battery terminal, then ran the engine, looked at the voltmeter and saw about 13.3 V. I also then temporarily connected a wire from the alternator terminal for the fat red wire straight to the positive battery terminal and got up to about 13.8 V. Seems to me the alternator is working.

Figuring that indeed my several-years-old alternator-wire fix needed re-doing, I replaced the skinny red wire but was back to 12.8 V. Seems the 13.3 V was somehow attributable to directly connecting the the alternator terminal for the skinny red wire straight to the positive battery terminal...

I'm lost and I bet this is easy. Please tell me how to fix this!


Use a voltmeter to find the voltage drop.

Connect the voltmeter to the alternator case and a good engine block ground. The voltmeter should read less than 0.3 volts. Now connect the voltmeter from the engine block to battery negative, should be 0.3 volts or less.

Now connect the voltmeter to B+ terminal on the alternator and the other meter lead to the battery wire on the starter. Again the meter should read 0.3 volts or less.

Now connect the volt meter from the battery terminal on the starter to the positive terminal on the battery. Should see less than 0.3 volts.

Any connection that shows more than 0.3 volts needs cleaned or the wiring may need replaced.
Use your ohmmeter to check the exciter wire (skinny red wire). The exciter wire comes from the battery charging light in the instrument cluster. The light gets its power from the ignition switch. Also check the junction block under the hood, follow the small wire on the battery positive terminal to the junction block. Disconnect the battery. Then lift straight up on the junction block cover. Check the wiring in the junction block, it should be clean and tight connections. From the junction block power goes to the ignition switch and fuse block. Also check all fuse connections, the fuses often corrode. Remove them one at a time and clean the terminals and fuses. Use dielectric grease on all connections to prevent future corrosion.
last summer I discovered that my car would loose charge over night and not start in the morning! So I would just disconnect the battery over night so I wouldn't have to jump start the car in the morning, I finally check the voltage at the fuse's and found that there was a draw from the relay that runs the courtesy lights and all! My car is a 91' and I took a relay from my 93' and replaced it, but it didn't not work ( I hope it was just something to do with a change they made for 1993! Idk know if that is too far out there but it sounds familiar!
- HUGE SNIP- Use dielectric grease on all connections to prevent future corrosion.

WHY *dielectric grease on all connections*??

look up *DIELECTRIC* in the dictionary... (go ahead... I'll wait....)

this is one of the "OWT that is just plain WRONG"...

you want a CONDUCTIVE ANTI-OXIDANT PASTE on those joins..

Burndy Penatrox P8A: http://westsidedelivers.com/item.asp?PID=14189

Ideal Noalox : http://idealindustries.com/prodDetail.do?prodId=noalox&div=5&l1=accessories

Kopr Shield : http://www.epinions.com/review/KOPR...er_Surface_Treatment_epi/content_479258054276

GB OX Gard: http://www99.epinions.com/review/Ox_Gard_Anti_Oxidant_Compound_OX_100B_epi/content_479252942468

I have and use both BURNDY P8A and Kopr-Shield to great effect (both cars and bikes..*and * Marine applications ):nod:
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