In a past life I had a 67 GTO, that had been "re-wire" (butchered) by the PO. Turn on the lights and the temp pegged, the oil pressure dropped to zero, when the wipers were on the dash lights increased/decreased in brightness in sysnc with the movement of the wipers. Tried troubleshooting -- ended up just getting a manual and rewiring everything under the dash -- in process found a faulty ground. If you have an electrical diagram look for any commonslities between temp sensor and light circuits.
