TR6 Purple/Red wires & mystery bulbs

[pdplot]

Fastening up a new drivers side air hose, I spied a couple of purple & red wires leading to a female connector. I see no corresponding male connector. Any ideas what this is? I need a magnifying glass to read the wiring diagram. Could it be for the seat belt buzzer that I removed 20 years ago? I also found a couple of small bulbs hanging there. How many illumination bulbs plug into the tach and speedo? The instrument lights seem to work but dimly.

 

[Gliderman8]

Could they be the footwell lights?
They might be the two lights that illuminate when the doors are opened. Just a wild guess without looking at a schematic.

 

[pdplot]

Don't remember any footwell lights. I did install a couple of lights on either side of the gearbox tunnel with a switch on the dash panel. They use red wires.

 

[Gliderman8]

My '73 TR6 has a hanging bulb over each footwell. If memory serves me they are violet wires and are activated by the door switch.

 

[TR3driver]

On some years, I believe there were two purple/orange wires that ran to the switch in the driver's A-post. Activated the key courtesy lamp and the key-in warning buzzer (if the key was in when the door was open).

I believe there should be 2 dash lamps each in the speedo and tach. Also some indicator bulbs, 2 per instrument IIRC. Oil, ignition, turn and high beam (maybe).

BTW, if you have the PDF version of the wiring diagram from the AAW site, you can zoom in with Ctrl-+ I use that a lot ...
Hmm, well, it works on Windoze. Might not work on other devices, especially those without a "Control" key

 

[pdplot]

Thanks, Randall. I think you're right on the wire colors. It looks more like orange than red. I'll check the door post. I disconnected the buzzer many years ago because it was a PITA and unnecessary. The hanging bulbs seem very dim but since I can't really lay under the dash any more, I don't know where they go and every time I poke around under there, other bulbs seem to pop out and have to be sorted by trial and error. Lucas again. Also - the brake warning light doesn't seem to work. I checked the switch below the master cylinder and the plug-in terminal was corroded badly. I filed off the corrosion and reamed out the hole but it did not seem to help. How can I test the switch to see if it works? I tried jumping the wire directly to the battery with a test light but no joy.

 

[TR3driver]

The PDWA (the whole assembly that carries that switch under the MC) should ground the wire to make the light come on, so connect a jumper from the wire to ground and turn the key on. If the light stays off, there is a wiring problem (or a bad bulb).

The PDWA should only actuate when there is a significant difference in pressure between front & rear; what are you doing to actuate it? Once actuated, it has to be manually moved back to center (which is a PITA).

But if you found a bunch of corrosion on it, most likely the switch doesn't work. IIRC it isn't really a switch anyway, just a spring-loaded plunger that contacts and completes the ground through the moving spool piece.

 

[pdplot]

OK. Will do. I also bought a continuity tester to replace one I had that fell apart. This one is sturdy.

 

[pdplot]

I connected wire to battery ground & turned on ignition. No dash light. I then put my 12V test light from the wire to battery positive. The test light lit brightly. No light on the dash. When I turned on the ignition, the test light dimmed from the positive terminal. Still no dash light. Any idea what all this means?

 

[TR3driver]

Does your oil pressure light work? Also, what year is your car? (Sorry, I forget)

The oil pressure switch and lamp are effectively in parallel with the PDWA switch, so your test light may have seen a path to ground through the oil light and OP switch (which would be closed with the engine off). To verify that, you can try pulling the white/brown wire off of the oil pressure switch.

But I can't explain why the test light would dim if the PDWA bulb is burned out or not connected. Could it be hanging down behind the dash instead of in it's holder?

 

[poolboy]

When I turned on the ignition, the test light dimmed from the positive terminal.

With proper circuitry that part sounds normal...With the ignition key in the ON/RUN position, the voltage to the BRAKE lamp gets cut in half to 6 volts.
The other 6 volts goes to the low Oil Pressure warning lamp.

 

[pdplot]

The oil pressure light works normally. Lights up when ignition is turned on, goes off when engine starts.
It's very difficult for me to reach up to the top of the speedo to check if that bulb is in. It's a rats nest of wiring and cables.The hazard bulb works when the hazard switch is turned on but does not light as it did before when the ignition is turned on. Question - what warning lights should light up when the ignition is turned on? I can't recall. Now, I get the ignition light, oil pressure light, high beam indicator and direction signal light (both directions). When lights are turned on, the dash lights go on as well (but the rheostat has never worked in 20 years). Both red lights at the top of the speedo do not light up when ignition is turned on.

 

[TR3driver]

With proper circuitry that part sounds normal...With the ignition key in the ON/RUN position, the voltage to the BRAKE lamp gets cut in half to 6 volts.
The other 6 volts goes to the low Oil Pressure warning lamp.

Right. I was just thinking that, with the brake warning light burned out or disconnected, there would be no path through the oil light.

Having the oil light work normally must mean the brake bulb is in-circuit, or else someone has put a resistor in it's place.

 

[TR3driver]

Question - what warning lights should light up when the ignition is turned on? I can't recall. Now, I get the ignition light, oil pressure light, high beam indicator and direction signal light (both directions). When lights are turned on, the dash lights go on as well (but the rheostat has never worked in 20 years). Both red lights at the top of the speedo do not light up when ignition is turned on.

High beam indicator should only be on if the high beams are on (main switch on, dimmer switch on high). Only time you should see both turn indicators is when the hazard flashers are on (and then the indicators should flash in unison).

Sounds like you may have a ground issue in the dash, in addition to the problem with the brake warning. That would probably also explain the dim dash lights.

 

[pdplot]

Both high beam indicator light and direction signal lights are working normally. 4-way flasher working normally. Dash lights have never been very bright. Ground wire attached to thumbscrew on tach. Engine would not turn over without it. Prior to replacing the tach and speedo cables and air vent hose, every light was working normally and had been doing so for 20 years. My TR6 is a 1971. The only lights that do not come on when the ignition switch is turned on are the two large red lights at the top of the speedo. I know the right bulb is good because the 4-way flasher will illuminate the bulb and it flashes.

 

[TR3driver]

Ok, now I'm confused. I thought you meant the high beam indicator comes on when you first turn the ignition switch on, with the headlight switch off? That's not "working normally".

The only "bulb test" function is for the brake warning lamp (which I believe was mandated by the same US law that required the lamp in the first place); which is why it's wired in with the oil pressure switch. All of the other indicator lamps should only indicate when their condition exists (eg turn signal indicators only when turn signals are actually lit).

Here's a drawing of the PDWA circuit, with some annotations

 

[pdplot]

Sorry for any confusion. To make it clear, ALL bulbs except the two large red ones at the top of the speedo are working normally; e.g. high beam indicator only works when the light switch is on headlights and the floor button is pressed; ign and oil pressure lights are dim on startup as they should be and go off when engine starts and direction signals are working in sync with the switch and the hazard switch.

 

[pdplot]

OK - everything working except the PDWA warning light and the trip odometer reset button. I don't see where the cable plugs into the back of the speedo.
Finally - not that I need to now, but how do you change a warning light bulb? Seems impossible to remove.