You have some ground, but a dirty connection somewhere could be causing this ground loop problem. Get a wire. Ground one end real good, like at the battery negative, a bolt on the frame or engine. Take the other end and start touching ground connections, holding it there while you try the brake and see if your symptoms go away. Like hold the wire on the ground side of the air valve, on the ground blocks, etc. Be careful not to hold it on a hot side.

 

Especially if they were manufactured by the Prince of Darkness: Lucas Electrics!

Harley wiring is fairly straight forward with a few quirks. My 93 FLHS harness is simple compared to the FLHTC/U or FLTC/U.

Good luck: Circuit tester and VOM are your friends.

 

First off I truly appreciate everyone's comments and attempts to help. Secondly I don't mean to belabor this issue. As you can tell I'm stumped and frustrated. I want to be riding not wrenching

Yesterday I spent most of the day testing, cleaning, and looking for the problem. The two things I found was if I remove the taillight/brake light bulb The volt gauge loses power. I tested the wires at the anti dive solenoid and discovered ground wire would energize when the brake was applied. I disconnected the anti dive solenoid from the system and I still have the problem.
one more day and I'm going to admit defeat and take to someone else.

Thanks Roach

 

If you mean that the ground wire on the anti-dive valve has + voltage on it when you apply the brake, then your problem is that the anti-dive valve ground is not grounding properly. Trace that wire to the ground and clean the connection really well. Run a temporary ground wire as I suggested above to the ground wire side of the valve.

 

Thanks Doc. I have ran a temporary ground wire, still get the same power loss when the brake is applied. I even DCed the entire valve from the circuit, no change except the valve doesn't click when the brake is applied.

Im trying to follow your advise

Thanks from a very frustrated Roach

 

If you have a temporary ground wire on the negative side of the valve, then with the brake circuit energized or not, you should see zero volts on the negative side of the valve. If you see anything, you don't have a ground on it.

 

Just a thought, can you unplug/disconnect the harness that goes to the rear tail/brake light? The plug/connector probably has the rear directional wires, the tail light & brake light. I would reconnect the anti-dive valve. Now see what happens when you press the brake lever/pedal. Just wondering if you have a short in the rear harness (sometimes they come loose and can be rubbed by the tire). Do you get the same results by pressing the brake lever or the brake pedal? If you only get a problem with the lever than maybe a pinched/shorted wire in the right hand controls/harness. Again these are just ideas/guesses, something to try.

 

Thanks everyone for all the help. I'm throwing in the towel. Accepting defeat. Way too much time spent and way to much frustration with 0 gain.

Have a good day. I will not be visiting this threat again.

You guys have been great.