Frustrating Electrical Condition

I have a frustrating electrical condition with my 1974 911 coupe. When I switch on my lights, either running or parking, my console gauges jump. In particular, my temperature gauge jumps up approximatley 10 degrees. Anyone have a suggestion for eliminating this condition?

I had a somewhat similar problem w/ my tach on an '83SC. I swapped out the voltage regulator and the ignition coil. The coils very rarely fail, but are sometimes placed real close to the engine and can overheat over time...

I am not well versed on the 74 Porsche but it sounds to me that the lights are miswired and are somehow running on the same hot line as the other gauges.
When the lights are turned on it creates an additional path for current to travel thus reducing the resistance to the other gauges and causes them to jump. The increase on them temperature gauge is almost a dead giveaway since the lower the resistance the higher the gauge will read.

I too had a similar problem in my 73 911 and it turned out to be a cracked fuse block and striped wire that was allowing it to arc. I changed the block and all is fine. God luck with this one; electical problems are hard to track.

Check your ground strap at the front of the transmission. Check both ends of cable for tight connection.