Excellant forum guys with plenty of info. Ihope you can help solve my problem. I have an 89 with the I-6 and close to 200,000 miles. I was on a 2-hr journey during the day, had the fan blowing and as the trip progressed I noticed the voltmeter gradually dropping untill it showed 12 v. I turned off the fan and voltage went back up. I put a more accurate meter when I was home. The batt had 12.7 v with the truck off, after starting I noticed that alt. would only put out 13.7 v (no load and no increase with rpm) and with lights and blower drop to less than 12v. The alt. was rebuilt due to low charging voltage a couple months ago so I removed it and had it tested whereupon it showed more than 14v under load! I then cleaned all the alt, solenoid, battery and h/l ground connections. I retested and now I have 14.1v with either the h/l OR blower on but when both are on I can only get 12.9 -13.1 v. what am I missing here?

 

Where are you taking the voltage reading from, the battery or the alternator output terminal?

 

Just thought I would pass along that after noticing an improvement by cleaning the contacts between the alt. and battery I noticed that I forgot to clean the other end of the ground cable connection at the starter/engine block and guess what! I now have 14.4v under full load!

 

sorry hanky you must have replied while I was typing, I took readings off the batt. posts.

 

Glad you found and solved your vehicles problem. Thanks for the reply!,,,,,,hanky