Dr H. This is a new problem.
sx3x not sure I follow "Follow the orange wires to the breaker and jump across it." I understand following the orange wire to the breaker not the "jump across it"

Roach

 

The breaker will have two post with wires connected, you could use a screwdriver to jump across, which means to connect the two post together while applying the brakes to see if the gauges still drop out.
It's just a quick test in case the breaker is weak and disconnecting when loaded.

Be careful not to touch anything other metal when jumping across the breaker, don't want to do any arc welding

 

Sx3x
I get it now. I was being slow witted. I will give that a try

Roach

 

I've had success by first testing anything that reads Lucas on it

 

Lucas..... Prince of Darkness. I've had the pleasure of owning British machines as well.

 

If it's any help, many electrical problems are actually mechanical. That is to say they are caused by poor contacts, damaged wires, loose or rusty grounds, etc. So rigorous visual inspection can often find a suspicious feature that is the cause of the fault.

 

Well after a day and a half of looking, poking, and prodding, here is where I'm at.
With the ignition switch in the "Lights" position the "Volt and oil pressure gauges" works. When I apply either the front or rear brake both gauges lose power. Using a test light when I check the orange wire at the gauge it is hot all the time. When I check the black wire it does not have power. When I apply the brake the black wire is then energized.

So does this indicates a bad or missing ground? If so how do I isolate it. As I said above I have invested a solid eight hours in looking for it. I'm stumped

Roach

 

Black wires are usually grounds.'
Can you trace it?

 

I'm going with a bad ground, probably in the air anti-dive area. That runs off the brake light circuit.

 

I traced the ground wires to plug #7 A&B then to plug #5 A&B (per wiring diagram). Seems to be fine at those points.
The anti dive assembly solenoid valve is clicking each time I apply the brake.

Oh yeah now my self cancelling turn signal isn't working. It just keeps getting better.

Roach