[K15 Blazer Guy]

anyone else experience this?:
speedo and tach twitch and freak out under FULL voltage load
like, headlights, blower motor, etc etc

but only when i have the high beams on plus the low beams
http://www.summitracing.com/parts/prf-30802

otherwise its quite accurate... im lost... help!!

 

[Arbitert343GS]

Have you checked to see if the printed circuit on the back of the gauges is ok, I had a friend with about the same problem in his 69 and it was because the plastic printed circuit was melted.

 

[K15 Blazer Guy]

fixed it.
the main bus wire was over 6' long and had worn through somewhere....
new wire, new battery cables, fresh battery grounds. fixed