14 volts at the battery and alternator and 12 volts on the gage

on my truck the dash volt gauge was showing just above 13 but with lights, fan on it was below 13.trided several different readings, from nothing on to everything on, wrote down all the readings. then I took out the dash gauge, used my 12 volt tester to see which prong was hot, then put my meter on the correct prongs & went thru the process again. it showed the exact same as gauge, so I know know gauge is good.

then I started truck, put every accessory that I could think of on & put red lead on hot at back of alt/black lead at ground back of alt. got 13.9 volts. put leads on batteries got 13.8 looked at dash volts it read 12.5. I knew my alt/ batt & charging sys was good. I disconnected my battery cables, so no current would be in the wires. I then hooked my continuity tester to each prob on the dash gauge & after about 15 min of tracing ground & hot from dash to where they went, found the hot wire from alt going to dash gauge, was corroded real bad & more than 1/2 of the wire strands were broke. cut out bad wire, replaced with quality wire connector, sprayed corrosion eliminator on it. siliconed it & shrink wrapped it. all is showing good & accurate now. with my intl coe it is more difficult to fix these kind of problems, need ladder, long arms e.t.c. I do not know if I went thru the right process to fix this, or if I could of done it a different way, but it did work, at least for now. I will not be going on the road til mon, to do a real test.

 

Yah, good to hear. Who knows what happened in the past. Lots of wiring gets monkeyed with. In order to save $10 per truck, some manufacturers have batteries connected by pairs with each pair having it's own positive cable to the starter. So with a typical 4 battery truck, only 2 pairs of batteries are connected in parallel in the battery box and the two pairs makes their final connection together at the starter from the two main battery cables. What happens is one of positive cables, or ground starts to go bad so that pair isn't really charging normally or providing properly during crank. Eventually they get so weak that weird stuff starts to happen. The cab and or engine will draw off of one pair or the other from the battery box. Murphy's law says the pair the engine draws from is also the pair with the bad cable and not charging properly. So to prevent this, a $10 battery to battery jumper is all you need to ensure each battery is connected to each other to eliminate issues like this.

 

Having the same exact problem on my 05 Volvo. could one bad battery cause this.