1985 Carver 3607 Tach issues

[3607Dave]

I have an issue with the Tachometers on the bridge and lower helm. All 4 of them do not work, the synchronizer gauge on the bridge works. There isn't one at the lower helm. I would think is would be bad ground from the engines some place. The synchronizer gauge works. That right there leaves me If anyone can clue me in how they all work together. That would be a great help. Thanks

[waybomb]

Try this. On the back of the tach is a small selector ( for selecting 4. 6, or 8cyl) you can turn with a small screwdriver. Move it back and forth a number of times.
The contacts may be corroded. This cleans them up. If the synchronizer is getting a signal, so are the tacks.

[3607Dave]

I'll have to give that a shot on the bridge. I did get a real crappy shrink wrap job last winter. The wiring diagram in the manual is useless. Makes sense if the tach signal comes from the bridge, Thanks David