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MGB Electric problem '75 MGB

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ceedub

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I have a small wiring problem with my "B". When I turn on the headlight switch, the tachometer quits. All lights are working OK. I suspect that it is a ground problem, but I am not sure where to look for a solution.
 
Yours is the last tach type produced and is on cars from '74 on. It has a 12v connection and an input connection that goes to the negative side of the coil. It is grounded through the case of the tach. Look here: https://www.mgcars.org.uk/electrical/last_tach.html You might have a loose connection at the tach or where it connects and, when the lights go on, the bulb in the tach loads the circuit down so the tach wont work. The tach connects directly to 12volts and doesn't connect to the regulator because the regulator pulses and would effect the tach reading.

Bob
 
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