Front battery not charging

[Chuckanut]

Hey guys, I have a weird issue I have a vdo 4K tach in my truck that stopped working when you turn the key the needle moves up to zero and when you turn on the engine the needle goes up to 200 rpm then back down to zero but never holds at 200 RPM just goes up and goes back down when you turn the key. Then the following day the truck would crank a little more than usual to start usually it’s just a flick of the key and I thought that was strange and then that night the truck wouldn’t start it just would make the starter start clicking like a jackhammer like it wasn’t getting enough voltage and I checked I only had 19 V. The volt gauge still works. But then I noticed that when I turn the key both the generator lights don’t come on only number two does Gen one comes on but it’s really dim it almost has to be dark out to see it, The number two battery is holding a charge at 16 V and when I put it on a battery charger it says it’s 90% charged when I put the number one battery on it says it’s only 30% charged. When my tack first stopped working I checked under the hood there was continuity through all the wires and I was just messing with the wires seeing if it was just a loose wire or some thing and The positive terminal wire eyelet connector to the terminal had fallen off. Not the terminal but the wire connector . So we replaced bad and still the tach doesn’t work and doesn’t charge. It’s weird though because when the truck is running it sits at 32 V and when the truck is off after running it’s at 31 V and slowly goes up to 32 but over the course of two days it just stops starting and that’s when I check the voltage and it’s down to 19 V, we rebuilt the alternator about a year ago so it’s possible the positive wire arced and fried some thing in the alternator even though it says it’s putting out 12.6 V when the truck is running. What do you guys think?

 

[WWRD99]

Hey guys, I have a weird issue I have a vdo 4K tach in my truck that stopped working when you turn the key the needle moves up to zero and when you turn on the engine the needle goes up to 200 rpm then back down to zero but never holds at 200 RPM just goes up and goes back down when you turn the key. Then the following day the truck would crank a little more than usual to start usually it’s just a flick of the key and I thought that was strange and then that night the truck wouldn’t start it just would make the starter start clicking like a jackhammer like it wasn’t getting enough voltage and I checked I only had 19 V. The volt gauge still works. But then I noticed that when I turn the key both the generator lights don’t come on only number two does Gen one comes on but it’s really dim it almost has to be dark out to see it, The number two battery is holding a charge at 16 V and when I put it on a battery charger it says it’s 90% charged when I put the number one battery on it says it’s only 30% charged. When my tack first stopped working I checked under the hood there was continuity through all the wires and I was just messing with the wires seeing if it was just a loose wire or some thing and The positive terminal wire eyelet connector to the terminal had fallen off. Not the terminal but the wire connector . So we replaced bad and still the tach doesn’t work and doesn’t charge. It’s weird though because when the truck is running it sits at 32 V and when the truck is off after running it’s at 31 V and slowly goes up to 32 but over the course of two days it just stops starting and that’s when I check the voltage and it’s down to 19 V, we rebuilt the alternator about a year ago so it’s possible the positive wire arced and fried some thing in the alternator even though it says it’s putting out 12.6 V when the truck is running. What do you guys think?

I'm just gonna throw this out there that since that tach is not stock and not in the tm I'm not sure many people have any clue how to fix that. Is the VDO website have any diag or tech notes on how it is hooked up and how it works? The voltage should not be 32 volts as well...way to high. If the charging went out the same time as the tach maybe they wired it into the alternator for some kind of tach feed? I'd start with the sticky on how to diag the charging system and figure out what is wrong with it and maybe get lucky and stumble on the tach fix.