[Mgs] B/GT electrical problems

[PaulHunt73]

The fact that one has been intermittent for a while and the other only happened recently implies they are not the same fault.

The voltage stabiliser only supplies power to the fuel and electric temp gauges, not the tach.  The confusion with the tach is that the green supply to the tach is often daisy chained off the 12v terminal feeding the voltage stabiliser.  If all three were failing to register then it could be the green supply to the voltage stabiliser (and hence the tach) that had failed, other than that they are separate problems.

Because the fuel and electric temp gauges are fed from the voltage stabiliser if the stabiliser fails in that it continually supplies system voltage to those gauges then they will read high, and will vary as system voltage goes up and down.  The simple test for that is to switch on the ignition but don't start the engine, and note the fuel gauge reading once it has stabilised tapping the gauge with a knuckle occasionally.  Then start the engine and get it charging, and if the fuel gauge goes up then the stabiliser is faulty.

If the temp gauge started heading for H as soon as you switched on the ignition then the blue/green wire to the sender is shorting out.  But if it only starts rising once the engine is running it's more like something causing excess heat, perhaps low coolant causing boiling, other than that the sender may have failed in an unusual way.

If the tach stops working but the engine continues to run then it could be a wiring problem or an internal fault.  For the former either loss of the 12v or earth supplies to the case, or if anything has changed with the ignition coil wiring the power to the coil could be bypassing the trigger circuit in the tach.

PaulH.
  ----- Original Message ----- 


  #1 – tachometer – after working sporadically, the tach in my ’71 B/GT has finally quit completely.

  #2 – temperature gauge – until we started it up this spring, the gauge has never been above “N” (except for one long uphill crawl with a loose fan belt).  Now, after only a few minutes at idle, it went rapidly to “H”.
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