> Where does the third brown/blue wire come from
> and what does it connect to?
I don't know. But one way forward is to check that none of them are
touching ground, and then connect the battery temporarily. Use a test lamp
or voltmeter to discover which brown/blue is hot. That wire will have to go
to the ignition switch. If you want, you can connect it now and check the
rest of the ignition, as just that wire is enough to allow the engine to
run, gauges to come up, etc.
Then use your test lamp (better than a voltmeter for this test) between the
hot wire and each of the other NU wires. Should be no light. Turn on the
headlight switch, check again. The wire that now lights your test lamp is
the wire to the headlight switch and needs to be joined to the hot wire in
some fashion.
Then leave the third one disconnected until you find something that doesn't
work. That will tell you more about where it should go. One possibility
might be that some DPO has installed the wrong wiring harness and the extra
NU is simply extra. Even the diagram in my TR4 owner's manual only shows 2
NU wires.
> Also how do you know when
> a good voltage stabilizer goes bad?
Assuming it's an original type and off the car, my first check would be for
continuity between the B and I terminals. No continuity means a defective
unit. Then apply 12-15v across the case and the B terminal and connect a
test lamp from I to the case. The test lamp should start flashing on and
off after a few moments. If so, I would say it works well enough, and
install it on the car.
If it is already installed on the car (and wired), a quick test is to
connect a test lamp or voltmeter across one of the gauge senders. Turn the
key on and wait a few moments. If the lamp starts flashing on and off
(voltmeter goes between 12v and 0v), the stabilizer is working.
There is another test you can do to check the "stabilizer"s calibration, but
IMO it's more of a pain than it's worth. These gauges were never all that
accurate to begin with, so if it's off a bit, that will be "as original".
If you want to improve the accuracy of the gauges, then calibrate them while
using your particular stabilizer in the circuit.
Randall
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