Help... Adding a second temp gauge

[Brian Bearor]

I tried install a Bosch temperature gauge but the needle is bouncing continuously.

My goal was to splice off the factory temp gauge and add the second Bosch gauge where both of them would be operational.

Trying to diagnose I isolated the line to the power, sensor, and ground with no luck. I did this by using a long wire with roach clips on both sides. I first tried to go directly from the gauge to the sensor, then to the ground on the battery, then to the positive side on the battery, and I am still having the same issue.

Any thoughts?

 

[halifaxhops]

Might need a diode in there so the gauges dont feed back into each other. Also is the bosch sender rated the same in ohms?

 

[Dana67Dart]

I think using 1 sender for 2 guages is only going to be a bad result.

The sender (typical aftermarket) uses a variable resister to cause the guage to move, adding a second guages to the system changes the resistance of the system.

The factory sender does the same thing but the supply voltage to the guages is not a continuous voltage it is a square wave, 12v on then off then on then off etc, the average voltage is in the 5 to 6 volt range. That is probably what you are seeing with your new guages fluctuating

 

[Scody21]

If you have 2 water ports, would be better to use 1 electric and 1 mechanical gauge. As the others have said running 2 electric gauges from the same sending unit is asking for problems...

 

[67Dart273]

There are several issues here none of them can be good
1....The original gauge is heavily damped so as not to show the pulses of the voltage limiter/ regulator.
2....The Bosch appears it might be a different design known as a "bridge" circuit, completely different
(3 terminals one of them grounded)
3.....It is very unlikely that the two meters use the same sender RANGE and therefore would never be accurate
4....As noted above, interaction between the two may make both inaccurate

You have to realize that the original gauge is a form of simple ohmeter working on current. When you change that current flow by adding a second load to the sender you are likely to upset the applecart. "Ohms Law." You have created a parallel path with more current flowing through the sender. For all I know it might be enough to damage the sender or at least affect it's accuracy because of the added current flow

 

[jbcalhoun]

 

[jbcalhoun]

I added the spacer to have an additional port for the extra gauge. This is accurate and matches the temp of the existing gauge (both are aftermarket gauges)