deadhead Posted May 14, 2009 Report Share Posted May 14, 2009 well, I am new around here, and have been browsing as a guest for a while, and now I have a problem that it seems like the knowledgable folks around here may be able to help with, so here goes.... I had to let my 1977 620 (king cab, california model) sit for around a year due to a carberatuer issue that I was finally able to resolve, and then I drove it for a week with no issues, until yesterday... As I pulled off the highway on the way home from work, I noticed the CHG light come on on the dash board. I ran it home as fast as legally allowed, and popped the hood. While driving home, I noticed that the light appeared to flicker at random moments, so my first assumption was a loose or corroded wire, so I had my wife sit in the truck watching the light while I wiggled every wire I could possibly move, and could not replicate any flickering of the light. So I jumped in it, with the intention of taking it down to the parts store to test the alt. and bat. and I noticed that I could get the light to shut off when the engine was up over 4k rpm or so, (no tach, just a "educated guess" based on the sound of the engine/travel speed). Got to the auto parts store, and put it on the diagnostic equip. and got the results, battery is good, and nearly full charge, and "no voltage detected" coming back into the battery. Tried the test again while maintaining enough engine speed to have the CHG light go out, with no change in the test results. The guy at the parts store did some part look-ups to see what was available, and since the voltage regulator was closer then the alt. we went ahead and ordered one, with the intention of "trying it out" before I paid for it to make sure that that was the issue. Fast foreward a day and a half, during which time I operated the truck a few times, even using it to take the backroads in to work, being careful to maintain as high an engine speed as possible by undershifting a little bit, trying to keep the charge light off as much as possible. I got it back to the parts store to check on the VR, but the guy who had ordered it originally was not in, and the other employees would not let me try the new one on before purchase for fear that I would just burn it out, so instead I opted to have a more experinced guy re-run the diagnostic, only to return nearly identical results, (the only difference is that the battery was now reccomended for charging...) So, I pulled the battery out, and tossed it on the charger at the store, and in the mean time, pulled the alt. out to get it tested on the dyno in the store. While I had it out, I noticed it was in less then perfect condition, but did not seem to be too damaged, and the dyno confirmed that it was operating well within the proper range. I put it back on the truck, and when the battery was all charged up, I put that back in too, fired right up, but the light was still on, so I tried pulling the + cable, and the truck died. If I am not mistaken, that means to me, that the truck was indeed running solely on battery power, (at least at idle), and indicated to me that the VR was indeed the issue,(I had also visually inspected all of the wiring coming from the bat. and connecting in any way to the alternator while I had a little extra room in the engine compartment so I went back in and bought the new one. I took it out the the truck, mounted it up, and turned it on. Now the light was still lit, but would not turn off at 4k, instead, I would have to push it up to (guessing...) around 7k to get it to go out. I took it down the street to a friends shop, and we got out the voltometer and test light, and got to poking around. We found that the bat. voltage was good, there was power going in and coming out from the alternator, the output at the VR harness seemed to be correct, and the CHG light would still not go out. I'm stumped. So my question in a nutshell, would be... Why is the CHG light on at low rpm, if the alt., VR, and battery cables have been eliminated as possible causes?????? Thanks for any suggestions or help you may be able to offer.... DAve oh, and does anyone know where to find a free wiring diagram for the 620 engine with external regulator? My mechanic friend was pretty sure he could find the problem with access to one, although neither of us can find one.... D Quote Link to comment
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