This is a weird one. The Hazard relay on my new project car clicks all the time. When you pull the flasher switch it clicks louder and the flashers work as they should. Where should I start?

What year? With a good wiring diagram, check why the coil on flasher relay is always getting power and activating. Work your way back to the source. The diagram will tell what to expect on each pin of relay.
If the coil is stuck closed the lights will operate normal when you pull the switch.

It's a 74 2.0L. I have one of those enlarged color wire diagrams. My eyes can't read those crapy Haynes diagrams.

Attached is the simplified schematic/wire diagram for '74-'76 914 with some electrical leakage path to ground. The OEM 914 flasher relay is designed to flash normally with very little current draw. This is so the MC brake warning and ebrake warning lights can be flashed normally.

If there is some electrical leakage path to ground the flasher will click. The problem is finding the leak. Maybe try pulling out the MC and ebrake warning lights and make sure they are not causing the mystery clicking.

Besides the brake warning lights, the only items on pin 49a of the flasher relay are the hazard switch and turnsignal stalk and its wiring. If removing the brake warning doesn't stop the clicking, try disconnecting the hazard switch and or the turnsignal stalk.

That's a nice diagram easy to understand

reset switch on the master cylinder read all about it in the 914 "Tech Tips 700"

Previos owner did a bunch of work on the brakes. Bet that's it!