For those of you encountering this problem (either one pod or both
failing to operate), I have just recently gone through the rebuilding of
the motor/limit switch wiring of one pod and anticipate the same for the
other.
As an advisory note, the right-hand pod motor failed on mine not because
the motor had failed (note that many people simply wish to exchange the
motor, but that option is not available right now--both Rimmer Bros. and
Moss have a shortage of motors for rebuilding and do not offer the
part), but rather because the diodes in the limit switch failed,
catastrophically.
One diode shorted (allowing current to pass the diode in both
directions), while the other exploded. This latter occurrance would
normally create an open in the circuit to the relay coil, but, in this
case, the carbonized pieces of the diode lay together, effectively
creating another short. This, of course, creates a severe problem with
the 20A automatic circuit breaker in the headlamp operating circuit, and
causes it to overheat.
Note that from experience with auto-breakers of other makes in the past,
these breakers work as intended perhaps ten times and then begin to
degrade. As they give up, they themselves short and fry the wiring. The
original 20A auto-breaker seems not to be available from any source, so
another source must be found. Fortunately, the wiring connector for this
breaker is identical to that of a 20A standard ATO fuse. If one is
certain that the wiring in the headlamp operating circuit is okay, a 20A
ATO fuse can be used. If the wiring is not correct, the fuse will blow
repeatedly and one must replace it constantly. There is a German circuit
breaker of the same terminal type, which can be reset manually, and I
will provide the number for that when time allows me to obtain it.
The other change made during this rebuild was to change position of the
diodes. The diodes seem to be the weak link in the headlight operating
circuit, thanks to Lucas providing diodes of substandard reverse current
capacity. My guess would be that the diodes have a rating of about 50PIV
(peak inverse voltage), and that rating is not sufficient to withstand
the back emf created when one operates the motors by hand without first
disconnecting the motor harness. That action probably causes one or more
of the diodes to fail. (Those with a battery or battery charger handy
can determine, from the red/grn tracer and black/grn tracer wires if the
motor operates and discount that possibility of failure and proceed.)
The solution is to remove the motor and pod carrier from the car, remove
the cover from the limit switch area on the motor, note the wiring
positions and clip off each lead between each limit switch terminal and
the diode and discard the existing diode (those with a digital
multimeter capable of determining if a diode is good can still check,
but the following makes that unnecessary). Solder each limit switch wire
directly to each limit switch terminal, then route the wires out of the
limit switch area and apply silicone to ensure that the area where the
limit switch wiring enters the case is completely sealed.
The two wires from the limit switch terminations should then be
terminated in weatherproof connections (Deutsch or Packard/Delphi
Weatherpack are recommended). With terminals to match, a dual-diode pack
should be made up to splice between the main harness and the two wires
leading to the limit switch wires. Diodes used should be, at minimum,
2-4 amp with a PIV of 400V (probably available at the local Radio Shack
or its equivalent) and their terminations should match those from the
motor limit switches and the main lighting harness. Note that the banded
edge of the diode should, in terms of wiring direction, point toward the
limit switch.
Therefore, if, for any reason, the headlamp circuit fails in a way which
destroys the diodes, it is no longer necessary to remove the headlamp
pod/actuating assembly to replace the diodes (which can't be easily
done, anyway, because the diodes are crimped to the terminals of the
limit switch). In the event of future diode failure, one should only
have to disconnect the diode pack from between the headlight wiring and
the main lighting harness and repair the diode pack, instead of removing
the headlight pod/actuating assembly once again.
Replacement of the stock diodes with those recommended above should
prevent frequent diode failure, but in the event of diode failure, this
change should enable repeated repair to the most failure-prone part of
the headlight operating circuit quickly and more simply and avoid the
necessity of obtaining a rebuilt actuating motor assembly.
Note, too, that all the connectors provided for headlight lighting on
the TR7 are pretty bad by today's standards. My car spent virtually all
its life in Texas and _all_ the headlight and actuating connectors are
badly corroded. All of these will have to be replaced for the system to
operate properly, even if nothing else were wrong in the system overall.
Cheers, all.
--
Michael D. Porter
Roswell, NM
[mailto: mporter@zianet.com]
`70 GT6+ (being refurbished, slowly)
`71 GT6 Mk. III (organ donor)
`72 GT6 Mk. III (daily driver)
`64 TR4 (awaiting intensive care)
`80 TR7 (3.8 liter Buick-powered)
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