[Techno Duck]

I made a picture thread a year or so ago but it does not apply to the earlier interior car. I would say if the two ground points behind the fuse block (the most horrible location ever!) did not do the trick, consider replacing the battery cables. The blower motor and headlights are all high draw items and i bet you are getting some mega voltage drop going through those old cables.

I would replace everything..

-Battery to chassis ground
-Alternator to starter
-Starter to battery

and i would also add an extra ground cable from the engine block to the chassis.

When i replaced all the cables on my car it made a huge difference, the temperature and oil pressure gauge no longer bounced around when the fans kicked on or when i turned the headlights on. Also the voltmeter on the late cluster actually goes to 14v now when i turn the car on.. it never used to get much higher than 13v and would drop to as low as 12v with all the high draw items on.