Lake St. Clair Fishing Forum banner
1 - 6 of 6 Posts

3,406 Posts
Discussion Starter · #1 ·
My RPM Gauge has the needle stuck around 4k... It doesn't work anymore.
I have looked at the wires underneath the gauge, and they are all connected...
Should I just replace the gauge, or does someone know where on the engine I can check the connection. Is it off of the distributor????


3,691 Posts
If the needle doesn't move at all when you turn the key to the on position or bounce when you hit a wave I would guess that your tachometer is bad. Like you said, stuck. Even if you get it freed up it will most likely stick again.

The location of the other end of the wire goes to the ignition coil. The exact location varies depending on the year, manufacture and type of ignition. If it is an older point and condenser ignition the tach wire will be attached to the (neg) (-) post on the ignition coil. If it is a Chevy based engine with HEI or electronic ignition it will be plugged into the distributor cap or coil depending on year. If it has the larger (about 4.5" diameter cap) It's plugged into the cap (single small gauge wire). The newer electronic ignition smaller (about 3.5" diameter cap) it will be plugged into the coil. Truthfully it is always plugged into the coil. It's just that the coil is housed inside the larger Chevy distributor caps. The connector is on the outside of the cap.

If you are lucky enough to have a very new boat with distributor-less ignition and EFI, I believe that the tach is then driven directly from the engine's computer.

There are normally 4 wires going to a tachometer. 12+ (power), ground, power to the gauge light and the trigger or feed wire. Don't assume that because the gauge light works that the gauge circuit is getting power. You can check this with a cheep 12volt test light.

Clear as mud?

Good luck! Let us know what you find.

Premium Member
12,052 Posts
Like DY said.....its stuck. It happens all the time, on a couple of my boats. Rap on it and you should be fine.

81 Posts
Here's a list of coomonly used color's for marine wiring
the tach wire should be grey @ coil

Blk -Grounds-General
Blk/Brn -Pump Grounds
Blk/Red -Voltmeter Grounds
Blk/Org -Isolated Accessory Grounds
Blk/Yel -ignition stop
Blk/Grn -Water Level Sender Ground
Blk/Blu -Lighting Grounds
Blk/Gry -Nav Light Grounds
Blk/Wht -Battery Parallel Solenoid
Brown -Pumps-General, Bilge or Sump (Manually Switched)(Also alternator starter to Ign.)
Brn/Red -Pumps, Bilge or Sump
Brn/Org -Power feed to Auto Bilge Switches-Pumps, Fuel/Oil Tranfer or Priming
Brn/Yel -Baitwell or Aerator
Brn/Grn -Fresh Water Pump/Water Maker
Brn/Blu -Head Pump
Brn/Vio -Washdown Pump
Brn/Wht -trim pos sender
Red - Battery Feeds Unprotected
Red/Vio -Misc. Accy. Main Feed Protected (fused) from batt to trim panel.
Pink -Fuel Sender
Org/Blk -Audio System Feed
Org/Brn -Electric Head-Sanitation System
Org/Red -Wiper Port
Orange -Accessories common feed- Dist Panel to Acc switch-Anode Electrode-Mercathode
Org/Yel -Diesel Pre-heat
Org/Grn -Wiper Stbd
Org/Blu -Communications Equipment
Org/Vio -Navigation Equipment
Org/Wht -Wiper Center
Yel/Blk -Choke - Neutral saftey trans mounted
Yel/Red -Start Solenoid(starting circut), Neutral Safety
Yel/Org -Powered Ventilation, Fans
Yellow -Bilge Blowers -(also alternator DC output)
Yel/Wht -Rudder Angle Sender
Grn/Red -Stop Solenoid/Kill Switch
Grn/Yel -AC Grounding
Green -Bonding
Grn/Wht -Engine Trim in and or tilt down
Grn/Org -Engine Independent Trim down
Blu/Blk -Cabin Lights
Blu/Brn -Oil Temp Send
Blu/Red -Cabin or Cockpit Lights Port
Blu/Org -Engine Independent Tilt Up
Blu/Yel -Lighting Circuits to Remote Send
Blu/Grn -Cabin or Cockpit Lights Stbd
Blu -Instrument & General Lighting
Blu/Vio -Courtesy, Boarding Lighting
Blu/Wht -Engine Trim Outand/or Tilt Up
Light Blue -Oil Pressure
Vio/Red -Eng. or Generator B+ from Breaker
Vio/Yel -I/O Trim Up (ballast bypass)
Vio/Grn -I/O Trim Down
Vio -12v Ignition-Generator or Engine
Vio/Wht -Trim "Trailer" switch
Gry/Blk -Mast Light
Gry/Red -Spotlight Remote
Gry/Org -Docking Lights
Gry/Grn -Strobe or Beacon
Gry/Blu -Spreader/Flood Lights
Gry/Vio -Windlass/Winch
Gray -Navigation (running) Lights, Tach. Send
Gry/Wht -Anchor Light
Wht/Brn -Temp. Alarm or Indicator
Wht/Red -Fuel Alarm or Indicator -((Ignition module to Dist.)Mercury Thunderbolt Ignition)
Wht/Org -Fire Alarm or Indicator
Wht/Yel -Air Flow Alarm or Indicator
Wht/Grn -Water Press/Flow Alarm or Indicator - ((Ignition module to Dist.)Mercury Thunder
1 - 6 of 6 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.