RPM gauge

[Bacchus]

OK I think I'm getting a better (correct) understanding
I now believe the upper terminal with single gray wire us the one you neant marked " send" when viewing the marking under the wire?
The bottom right terminal with a "ND" showing... is that really GRND?
If so, that makes sense it is connected to other gauges. Still not sure what the jumper is there for or maybe used in the past.

Separate wire from sender to tach stillba worthwhile step to udolate where the problem is / isnt.

 

[captbuddy]

I think you are right about the other being ground but I didn't look under it after finding "send" under the other. But bad news is I check with the jumper straight to what I thought was sending unit. No change. When to remove sending unit and had water coming out. Obviously the temp sending unit. Inspecting those two brown wires coming out of connector there might be a slight difference in color. Anyway I have got to find where the other brown wire is going. Will keep you posted.

 

[captbuddy]

Don, I think I found it this time. I found another brown wire past the junction plug. It went to a 3 prong plug that plugs into the bottom of the alternator. I check the ohms from the gray wire to brown wire just before plug and got a good ohms reading. I then checked the ohms from gray wire to the lead in the plug and got same ohms reading. So correct me if I'm wrong but could it be contacts inside of alternator. If so, does that mean having alternator rebuilt or could I just take it apart to check for contacts.

 

[Bacchus]

If I understand correctly you checked ohms (continuity = zero ohms) from the g e gray lead @ bach of tach to connector and connector to plug at alt and confirmed continuity for the whole wire run?

So possible issues...
Simple first... clean both ring terminal & post at tach and spade terminals at alt to be sure signal is being sent to and received from brown/ gray wires. Remove and clean both male & female side / stud & ring terminal.
(I have issues w connection at sending unit spade terminals cleaning & a little conducting grease seems to have cured my problem)

Next are more complicated.
Alt may not be putting out proper signal... an auto elec shop should be able to test your alt and confirm if OK or not. Be sure to tell him/her it's the tach output you suspect.

Tach itself may be faulty??
Are there any adjustment (calibration) screws? Usually accessed thru small dia hole on backside. If so you might try adjusting calibration to see if it helps. You want to return to the same spot so important to nite position and adjust one dire tion say CCW noting angle / turns then CW past where you started counting single/ turns, then back to where you started. If no improvement tach may be bad. Never got into them so not much help. I'd start w mfg of tach to see if they offer any repair / calibration service?
Ask the auto elec shop if they test / repair tachs while there... or if they snyone that does?

 

[Maerin]

A bad or marginal diode can cause tach problems. You can test to see if you're getting any AC voltage at the alternator output. Set your DMM (digital multi meter) to low or auto-ranging AC voltage. Place one lead on the red post, the other on the ground post or black wire with the engine running. If you have a leaking diode, you'll read some AC voltage on your meter. If reads "0", the diodes should be OK.



Another test is to check for current through the alternator. A failing diode will allow a parasitic flow. Engine off- If you remove the red lead and you get an arc to the post, that's current flow and there's a problem. Not a foolproof test, and be CAREFUL you don't allow the red lead or a wrench you're using on it to ground anywhere, You'll be arc welding. A hall effect DC amprobe is much more reliable. Engine off, you should see no current flow on the red alternator lead.


If you have a battery disconnect switch and it was inadvertently switched "OFF" with the engine running, that can cause the field voltage in the alternator to collapse and it will create a ripple or spike that can damage the diode bridge. That would manifest in symptoms you're having with the tach.



You can DIY replace the diode array, or just have an automotive electrical shop do it. If the alternator is easy to access, remove it and take it to a shop to have it tested/repaired.

 

[captbuddy]

Thanks Steve

 

[captbuddy]

Guys, I took my jumper wire from sending unit on back of tach and attached it to the lead on the alternator. Cranked engine and rpm is working. Right now not sure if it is the three prong plug at the alternator end is bad or a break in the wire somewhere. Going try to tie into wire just prior to plug to see if it is plug. At least I know it's not the rpm gauge.

 

[rgano]

Nice to see such perserverence all the while getting a thorough education on this tiny portion of the boat. I think this boat is in good hands.

 

[captbuddy]

Ok guys. I have tied into wire just prior to plug and rpm does not work. Put another female terminal back on jumper and put back on lead at alternator. Rpm works. So it is obvious to me that for some reason the 3 prong plug is bad. Does anyone have any idea where I could get another 3 prong female like this one

 

[HTurner]

Try this:


https://www.repairconnector.com/products/Delco-SI-Series-Alternator-Repair-Connector-3-Terminal.html

 

[diver dave]

1/4” flags?
U need this:

Made for insertion (and holding) in molded plugs.

ps: Turners fix looks even easier! [emoji106]

 

[captbuddy]

Thanks Turner. I’m going to check one more thing before I order that but it looks like that’s my fix.

 

[captbuddy]

Thanks Dave. I agree on Turner’s find.

 

[captbuddy]

I just did my final check. I connected a short jumper to the original wire coming from flybridge with a single female terminal on the end. Cranked engine and tach is working. That shows me my Original wiring from flybridge is OK. It definitely is the 3 prong plug. Will be ordering the one Turner said. Can't thank y'all enough.

 

[HTurner]

I just did my final check. I connected a short jumper to the original wire coming from flybridge with a single female terminal on the end. Cranked engine and tach is working. That shows me my Original wiring from flybridge is OK. It definitely is the 3 prong plug. Will be ordering the one Turner said. Can't thank y'all enough.

Glad it a worked out.