I’m experiencing an intermittent problem with my '73 Toyota FJ40 Land Cruiser.
After I’ve been driving for a while (about half an hour usually), my headlights and dash lights will suddenly dim noticeably. I noticed that when it happens, my ammeter gage drops into the negative (swings to the left of center). I believe this indicates the alternator has cut out (stopped outputting current), and that all my systems (including the engine ignition system) are running off the battery.
Strangely, I found that stepping on the clutch—momentarily cures the problem! I.e., when I step on the clutch, the needle immediately swings back to the middle and all the lights return to full brightness. When I release the clutch, everything is usually ok for about a minute or two—and sometimes, it stays “fixed” for a lot longer (sometimes until I complete my journey).
Oh yeah, one more hint—this only happens when my headlights are on. It never happens when I’m just using the running lights, or when I’m running without any lights!?!
Any ideas would be appreciated.