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Bouncing Tach on Series III E-Type


Luke Skywalker
My father-in-law just called after picking up his new Series III E-Type Coupe. He said the tach is bouncing wildly, and asked me if it's electrical, mechanical or what -- to which I said "it's mechanical on some british cars, electrical on later ones, but I don't know on the '73 without looking."

I would suspect it's electrical and he has a faulty voltage regulator. He'll be here in an hour.

Anyone know off hand and suggest a cure?

Bruce Bowker

Obi Wan
I am fairly sure it is electrical with possibly a "generator" running of one of the cams. See if you can trace a wire.



Luke Skywalker
My in-laws came over with the car, and the tach is really bouncing wildly -from pin-to-pin. The clock doesn't work and the oil pressure gauge was just disconnected by the Jag dealer that had the car, because it was bouncing wildly.

I'd guess voltage regulator -- told my in-laws to order a new one from Moss.

It's a pretty fun car. Great engine note. Very narrow and feels small, but very heavy. I wouldn't want to rush it around a track!

John S Farrington

Jedi Warrior
The tachometer is electrical and uses the ignition to drive the instrument. It sounds like you have a defective tachometer but the other instrument problems conflict from that. I dont believe that the alternator voltage regulator could cause such a problem. The Jags use a voltage stabilizer for the dash instruments; this could be the source of the problem.


Luke Skywalker
This is why I like my TR3 -- there are two fuses and one regulator for the whole dang car. Pretty easy to track problems. (Plus only four spark plugs to change!)
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