i have functional hand brake warning light and blinkers. However, when I release the handbrake on my 1972 model, the light changes to a very weak blinking and I can hear the flasher clicking. The turn signal system is unaffected. If I disconnect the switch at the brake handle, it still happens, so the obvious switch failure is ruled out.

My first thought is a partial short to ground from one of the brown and white wires, but I wonder if it could be the relay/flasher itself? That would be easier than tracing for a frayed wire or connector touching the body.
Thanks.

Sounds like relay going bad.

Is that a known symptom? I kinda was thinking it might be and I did a pretty thorough overhaul of the wiring harness. The seatbelt warning light on the center of the dash was another suspect, but I have never figured out how that and the warning relay under the seat - long gone - actually work.

I don't think the flasher is at fault with your issue. Check out the schematic below. Notice that if both brake switches are open, there is no path to ground for the brake system warning indicator and thus when the switches are open, the lamp cannot light. I would assume there is some leakage path between the lamp and the 2 switches.

You can test this by removing the lamp and measuring the resistance to ground. It should be infinite. If you can't figure out which wire to the bulb is the wire to the brake switches, pull the ebrake and the wire to the brake switches will change to a low impedance.

Click to view attachment

Oh, I have looked at your schematic a lot! And had come to the same conclusion. I just hoped that a relay fault would be known to produce the symptom. I hate tracing things under the dash cause I don’t bend so well. The next scene will have me upside down with my feet on the targa bar.

Just pop off out the brake/GEN/Oil instrument to check the resistance of the wires to the switches. All measurements can be done while sitting in the driver's seat. At this point you're just looking to see that the impedance to the brake switches is zero or infinite. No need to get under the dash yet.

Thanks Jerry! My car came with yet a third set of brown and white wires taped off next to the brake fluid reservoir. I assumed that was provided in case they wanted a warning float. I added that from a 911. That works, but am afraid it doesn’t explain the problem. They were the easiest to disconnect, but the weak clicking still persists. I am almost certain they were stock, but haven’t heard much from others with the same wiring harness. Kinda hidden I guess.

I did that. I found a 0.7 ohm path to ground that appears to be rectified. Found that out by accident when I took off the lead to the brake switch and at first found infinite resistance to ground. But I tried it again with the black and red test wires reversed and it has that short.
I think this is how it is laid out - from a post I made a few years ago:

http://www.914world.com/bbs2/index.php?act...t&id=516085

Spoke - can you tell me the best place to look?

I do not have the seat belt switches in place. I did however leave the warning light mystery module on the dash. I am going to try disconnecting that. Honest! I buckle up every time. I won't even go round the block without em.

I bought a new relay because it was easier than tracing wires. I didn't put it in because while it was shipping I found a solution.

There is a connection between the brake warning circuit and the seat belt warning light module. When I overhauled everything I left that module in place, but the seat belt wiring was long gone. There must be a weak path through ground through that little light on the dash. Since it is a little plastic box with a rectangular fasten seat belt light, I don't know about the internal circuit. Wish I did.

At any rate: bottom line is I unplugged it and that seems to have fixed things. I get blinking when I should and no weak blinking clicking when I shouldn't. So that is something to tuck away. Which is good.