Sierra rev counter

[dandan62]

Stupid stupid! I did a job that involved removing the coil. I put in back 180 degs off by mistake so connected everything back up in reverse. Went for a drive. It ran fine surprisingly! Then noticed the rev counter only reading about half the revs. Got home checked coil and saw my error. Put it all back the right way around. Sadly the rev counter is still only half reading and sluggish. I have double checked all connections. Have I ruined it? Any ideas anyone? Anyone got one in that bin in the corner of the shed for me?

[Davo]

Is it an electronic one? Mine has a number of setting depending on how many then the dizzy does per engine revolution. If it is one of these could have gone back to factory settings. 
 

I think these type work by measuring current fluctuations on the wire as the spark is made, I don’t think it makes any difference if it measures on the positive or negative side, only that the negative is normally better. In fact the instructions for mine say you should hook it up to the positive side where as the dealers says you should hook it up to the negative side of the coil. Both work but neg is better 

[dandan62]

Thanks for the reply. It's the standard Sierra electronic one. Not adjustable. I'm pretty sure it's something on the cb that's gone because of the miswire. There are several capacitors. Not my field sadly. I've tracked down a replacement which should be here soon. Hopefully it will work. 

Cheers. 

[dandan62]

I received my replacement rev counter. Sadly I have the same issue. Only reading about half revs. I'm confused now. I suppose it's possible it has the same fault. I know these were fairly standard kit it early Sierra based kits so anybody any ideas? I would have thought either a coil produces a signal or doesn't. Can it have a fault to give only half a signal? Excuse my ignorance... 

At least I now have a spare set of instruments! 

[dandan62]

Update. I have come to the conclusion the replacement has the same fault. The whole cluster was sold as spares/repair so it was a gamble anyway. Googling shows it to be a common issue on these old Sierra rev counters. Probably an easy fix for someone with electronic knowledge and an oscilloscope! I've bought a cheap modern replacement which works fine. I'll eventually replace everything with matching instruments. Nice winter job!