Boost gauge faulty?

[robertverhey]

I am trying to trace a fault in my boost gauge circuit that causes the needle to snap to full deflection (1.0) as soon as the ignition has been switched on

I have read all that’s been written on the forum about bad earths on the transducer etc. all that checks out fine. But i’m starting to suspect the gauge itself. There appears to be an almost complete short internally between the + terminal and the G terminal (the latter which goes to the transducer). So the G terminal is getting a measured 7 volts even before the engine is started, which appears to be enough to snap it to a 1.0 reading.

Am I on the right track in diagnosing this? Would rather know before spending the big bucks on a replacement gauge.

If anyone has a known good gauge at hand and could measure the resistance across these two terminals it would be most appreciated. I’m getting .13ohms as per pic, and 7v at the G terminal with ignition (not engine) switched on

Thanks

Robert

[KenS]

I have measured a working boost gauge (replaced because of crackled black paint on the dial), I get 135 Ohms across the two tabs as in the photo in either polarity. Are you sure the meter is not measuring in K Ohms before scrapping the gauge?

[robertverhey]

Thanks for this, yes you are correct I had the meter wrongly calibrated..DOH! 131 ohms

However the good news is...PROBLEM SOLVED!

Ended up being something infuriatingly simple, the transducer had been mounted upside down and then the rubber cover fitted right way up, so what was actually showing as G on the rubber cover was actually WK on the transducer. Once I swapped the wire across to the correct G pole the gauge started behaving.

[KenS]

Great to hear that you have identified the problem and its a no cost fix.