[TR] TR6: gauge LEDs and headlight switches

[Tim Gaines]

Despite some difficulties I'm making progress in installing LiteZupp 
LEDs into the instruments in my 1974 LHD TR6. The difficulties stem from 
my (possibly foolish) decision to do the job without removing the dash. 
With the help of a couple of long-reach needle nose pliers I've replaced 
the two illumination bulbs in each of the speedo and tach and the single 
ones in the temperature and oil pressure gauges, not without several 
scrapes to my fingers. However, I really don't think that will work with 
the fuel and temperature gauges on the right. There are just too many 
obstacles, so something is going to have to be removed, likely either 
the radio or the glove box or both. It looks to me as if the glove box 
space would provide the best access, but I have read of some 
difficulties in getting it back in place after removal. I would 
appreciate any advice from those who have done these bulb replacements 
or taken out the glove box.

In the process of doing this bulb job I came across another problem. The 
new LED for the high beam indicator just wouldn't light, and it didn't 
matter which of the new LEDs I put in. So I went back to the old 
incandescent bulb and it didn't light either despite having worked a 
short time earlier. After checking the wiring to the socket and finding 
no issues I decided that the problem must be the iffy headlight dimmer 
switch on the right side of the steering column. I say "iffy" because 
occasionally I had found that switching to high beam left me with no 
headlights at all! I took off the plastic cowlings and got access to the 
switch though I couldn't pull it out because its wires are clamped 
within a channel under the steering column. Nevertheless, I could pivot 
the switch out to get a narrow view of its innards and insert the thin 
nozzle from a can of WD40, hoping for a lucky fix. The result was that 
the switch, when re-attached with its retaining screws, would now pivot 
toward me, something it never would do before. With the battery 
re-attached as well, that pivot action produced a high beam flash that 
also lit the beam indicator! I never knew I had a high beam flash in 
this old car! So, everything was fixed!? Not so much. The light switch 
on the dash wouldn't give me headlights at all despite the fact that it 
would give me interior lights and the other exterior ones.

It was time to get out Dan Masters' guide to electronics, and as always 
with this manual, I now understand the circuitry and my remaining 
problem. When everything is working, the flash function of the dimmer 
switch takes voltage from a fuse to the high beams directly regardless 
of whether the light switch on the dash is set for headlights. When the 
dash switch is set for headlights the voltage is taken directly from the 
battery to the column switch that determines whether low or high beams 
are activated. In following Masters' troubleshooting steps, I found that 
my dash light switch was bad. It must have failed as I repeatedly 
flipped it off and on to test all the new LEDs going in! I removed it, 
verified with a meter that it was bad but managed to clean it up inside, 
and it now tests okay. Today I plan to spray some electronic contact 
cleaner (not just WD40) into the dimmer switch and hope that all of its 
settings will work okay after I put the dash switch back in.

I'm sorry for the diversion into headlights. What I really want to know 
now is how to get those last two gauges illuminated with new LEDs.

Tim
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