Graphic Display - Electrical Troubleshooting Escort

Maybe there's a Ford mechanic somewhere that can point me in the right direction.

I have one of those graphic display modules that were popular in the late eighties and early nineties in the console. When I use the right turn signal, hazards or brakes the "brake light" led indicator lights up, even though I have verified that the rear brake light is working.

The bulb is a dual element that is used as the tail lamp and the brake/turn/stop lamp sharing a common ground. If the ground were bad I think the "tail lamp" indicator would also light up on the graphic display due to an interruption in the normal flow of electrons. I've ruled that out.

The graphic display has "rh brake light ref" and a "rh brake light sense" inputs. Not sure what these mean, but probably "reference" and "sensor". I have verified with a test light that the "rh brake light sense" input is getting the same signal as the hot wire going back to the brake light. The signal originates in the multifunction switch on the steering column. I don't think the "rh brake light sense" wire should be getting this signal if the light is working.

Looking at the electrical schematic, there are two splices off of the hot orange/blue wire going back to the tail lamp, one going to the "rh brake light ref" input and the other going to the "rh brake light sense" input on the graphic display. In between the two splices is shown to be a "resistance wire" spec'd to be 0.248 ohms. How this circuit is supposed to work is really a mystery to me.

Just wondering how these two splices and resistance wire work with the brake light hot wire and graphic display inputs, or simply, how the electrons are supposed to flow.

I pulled another graphic display from the junk yard and plugged it into my car and the same symptoms appear.

Thanks, Matt

Reply to
sleepdog
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Here's an ASCII schematic of the circuit I'm debugging. It's the tie in for the graphic display to the brake light wiring. Escorts without the graphics display option just have the brake lamp wire running straight back from the multifunction switch to the bulb.

The \ / chars represent the resistor wire. (1) goes to the "rh brake light sense" input, (2) goes to the "rh brake light ref" input to the graphic display. The "V" represents the flow of electrons, per the schematic.

So far I have figured out that (1) is getting the same signal as the brake/turn/stop lamp, so the LED in the display is on when I brake, blinks when I signal right turn, and blinks with the hazards. It didn't do this originally, and I checked out another graphic display from the junk yard with the same symptoms appearing. So I figure something between the two splices is not right, not sure.

I don't know how the circuit below works to sense trouble with the brake light, so not sure what to look for when I find the wires under the dash. I figure if the bulb was out the flow of electrons would not find a path to ground in the normal manner and instead go through the display module? I have replaced the bulb just to be sure.

Multi-function switch | | V splice ----------------- | | \ | / 0.248 ohms | \ | / | splice--------- | | | | | V V | (1) (2) | V brake light | | Gnd

Reply to
sleepdog

Great, google shredded my ascii art! The wires coming out of the splices are independant, do not contact one another.

Reply to
sleepdog

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