Guages

[BLAGERGREN]

I have a 1974 36' trojan. Fly bridge model. I put 4 new guages in the upper helm, (water & oil pressure). Now the upper helm and the upper helm are reading differently, i did not change the lower helm guages or the sending units, does anyone know what might have caused this or how i might fix this?

[jwrape]

That's good question, I have a 74' F-44 Motor yacht and 3 out of the 6 flybridge gauges don't work and one of the temp. gauges reads about 10 degrees cooler than the other. I need the same advise that you are looking for. Hopefully someone knows.

[Safari]

I would think that when you change gauges, you would want to match upper and lower gauges exactly - due to the fact that one sender is feeding both gauges. Any difference between the old gauge and the new gauge will be amplified - both gauges will be inaccurate.

[ken bogdan]

I'm having all kinds of guage problems and it appears to be a grounding problem. I have a 77 F32 and I'm guessing the previous owner(s) jerry rigged some of the wiring at some point and I can't find the short. I found someone in South Jersey who works on DC systems. If he works out, I will post his info here.

[prowlersfish]

Being they are new gages I would say they may not be matching to the senders . diffrent gages many need a difrent range sender one brand may use 0-90 ohm sender another may be 45-150 ohms etc.

Also make sure you a good gound on the gages a poor ground is the most common problem

[Obaby]

Never looked but is there an adjustment on the back of the gauge? Adding another gauge in series would increase resistance and effect both readings lower. Addind in parallel would decrease the resistance and increase the reading.
Therefore there must be a sliding parallel resistor to balance the gauges. Is there anything in the schematics?

The sender should be linear, best way to check the gauges and sender is with an older ohm meter. (most older ones are non-autoranging ) but do check those grounds !

Patrick

[Danny Bailey]

Paul is right...the gauge resistance has to match the sender resistance range and there is a different sender for single or dual gauge installations.

[mtwolf]

The eariler Trojan's used A/C Guages. Your best bet is to call Marine Tech 717-684-4145. When Trojan was sold, in the early 90's, some of the employees bought the stock of parts and started Marine Tech. You have to have the senders match the guages and Marine Tech is the place to call. They may not answer early in the morning so try later. If anyone can help you, it's these people. They are the go-to for Trojan!

John
73 F-31

[mr elevman]

allso with regards to the senders senders are either for single or dule station

[rossjo]

The resistance changed.

All 3 gauges should be the same mfgr/model - and you may need to calibrate from an infrared gun.

Back in the day, it was often necessary to tweak in gauges with small resistors in line.