Trojan Boat Forum

my f32 flybridge AND helm station oil pressure and water temp. are pegged to the right and other various positions.

can ANYONE point me in the direction you feel i should begin looking for my faulty ground wire??

very frustrating!!!!!

You have a short to ground on one of your connections for those gauges. The gauge works by sensing a change in resistance of the sending unit. If there is a short to ground on the sending unit or the wire coming from it to the gauge then there is no resistance and the gauge will peg at max reading. It is either a bad connection, bad sending unit. Do the gauges return to near zero with ignition off? Otherwise the gauge is bad.

What year? And for all temp/oil gauges- port and starboard?

There will be 4 terminals at the back of each gauge.
1- Illumination lamp- Blue wire for all gauges.
2- Ground- Black- shared by all gauges and terminates at ground block behind instrument panel.
3- Sig/sense- Lt. blue wire for port oil
Sig/sens- lt. Blue wire for starboard oil
Sig/sens- tan for port temp
Sig/sens- tan for starboard temp
4- Ignition will be color purple for all gauges.

Check the wiring from each sensor, oil pressure and coolant temp. You can try disconnecting each wire separately and see if any of the gauges come by to life. Hope this helps.

no they do not return to zero when ignition is off. it is a '75 f32 and it is both starboard and port, upper and lower stations.

Basic Troubleshooting of Gauges:

All Gauges:

1. Remove Sender Wire from “S” Terminal on Gauge, and Turn ON Instruments Circuit.

2. Test Voltage between “I” Terminal (External Power Supply) and Ground Terminal “G”.
Tested voltage must match nominal voltage of the Gauge (ie: 12V Gauge must test between 10 - 16VDC), and the Battery Voltage.
If no voltage - check Ignition or Instrument Switch(s) and/or Fuses.
If tests less than battery voltage, repair or replace (Violet) wire from Ignition or Instrument Switch.

If a Sender fails “Open” (Infinite Resistance), one or both (if Dual Station) Gauges will read Zero Scale.
If a Sender Fails “Closed” (shorted - Zero Resistance), one or both Gauges will read Full Scale.

Other confusing Ohmmeter results, such as readings lower than expected, could indicate a poor Ground Connection at the Sender Body (Sender to Engine Block). Check for pipe dope or tape on Sender Threads.

Temperature Gauges:

1. Disconnect Tan Sender Wire from Gauge (Terminal “S”) and turn Instrument Power ON.
The Temperature Gauge should indicate ZERO Scale (< Low Temperature).

2. Short the Gauge Sender Terminal “S” to Ground Terminal “G”.
The Gauge should deflect to FULL Scale (> High Temperature).

3. Measure Resistance from Tan Sender Wire (disconnected from Gauge) to Ground.
American Temp. Senders will read: 450 Ohms (Engine Cold @ 1000F)
or 29.6 Ohms (Engine Hot @ 2500F )
European Temp. Senders will read: 281 Ohms (Cold @ 400C) and 22 Ohms (Hot @ 1200C)

4. Disconnect Tan Wire from Sender on Engine Block.

5. Test continuity of Tan Wire.
Zero Ohms from Block End to Gauge End - If not, repair or replace Wire.


6. Measure Resistance from Sender Terminal (on Block) to Ground on Block.
Should read as per (3) above - If not, replace Sender.

Pressure Gauges:

1. Disconnect Dark Blue Sender Wire from Gauge, and turn power ON.
The Pressure Gauge should read ZERO Scale (Low Pressure).

2. Short the Gauge Sender Terminal to Ground.
The Gauge should deflect to FULL Scale (>High Pressure).

3. Measure Resistance from Dark Blue Sender Wire to Ground.
American Press. Sender: 240 Ohms (Zero Pressure) 33.5 Ohms (Full Pressure @ 80 psi)
European Press. Sender: 10 Ohms (Zero Press.) & 180 Ohms (Full Press. @ 150 Bar)

See 4, 5, & 6 above (but Dk. Blue Wire)

Fuel Gauges:

1. Disconnect Pink Sender Wire from Gauge, and turn power ON.
The Fuel Gauge should read ZERO Scale (< Empty)

2. Short the Gauge Sender Terminal to Ground.
The Gauge should read FULL Scale (> Full).

3. Measure resistance of Pink Sender Wire to Ground.
American Floats: 240 Ohms (Empty), 103 Ohms (½ Full), & 33 Ohms (Full)
European Floats: 10 Ohms (Empty), 95 Ohms (Half), & 180 Ohms (Full)
Automotive & other Float Switches may use other resistances such as 0 - 90 Ohm, 73 - 10 Ohm, & etc.

See 4, 5, & 6 above (but Pink Wire)

See also the graphics posted at:
Wiring Diagrams: http://cruisersforum.com/photopost//...php?photo=1622
Testing Instructions: http://cruisersforum.com/photopost//...php?photo=1623
Sender Resistance: http://cruisersforum.com/photopost//...php?photo=1624

would a bad wiring/ground on the flybridge affect the lower station or could it be a mis-matched sending unit/gauge.

Yes any dual gauge system would be affected by a bad or loose ground anywhere in the system either up on flybridge or down below.

The sending unit must be for a dual station and the gauges should be the same type and match the sending unit as far a manufacturer recommendations.