New Harness, Dash & Gauge Gremlins

[stwilegar]

1972 Scout ii, 345 with Auto Transmission.

After purchasing another man's nightmare, I installed a new American Autowire harness. While I was at it, I installed a new aluminum dash from IHPartsAmerica which came with Isspro gauges. I manged to get the wiring installed and worked out most of the bugs....except...

I Installed a new electric fan that seemd to work properly prior to installing the new harness and gauges. Here's the situation:

1. From the coolant sensor I have installed 3 wires. A signal wire to the gauge, a wire to the fan relay, and a third bypass wire to run the fan whenever i see fit.

2. When all 3 wires are connected to the coolant sensor, the fan runs the moment the ignition is turned to "on" AND the gauge pegs out to max temp.

3. If the relay wire is removed, the temp gauge funtions properly.

4. If the signal wire is removed and just the relay wire attached, the fan functions properly and comes on at the right temp but then i have no gauge.

So, the guage works and the fan works as long as the circuits are not combined. When both wires are attached to the sensor, all hell breaks loose.

This problem has me confounded. I've checked the bypass wire to be sure its not grounded somewhere and every part of this system is new including the sensor, relay, fan, gauges and wiring.

Any ideas would be welcome. Thanks in advance from Idaho.

 

[Scoutboy74]

I'll admit upfront that I'm ignorant of electric fan wiring, so my questions that follow may or may not render this declarative statement unnecessary. Does the manual fan bypass wire need to connect to the temp sensor at all? Couldn't it connect directly to the fan in some manner?

 

[stwilegar]

Yes. In order for the fan to operate manually it needs to be in the circuit somewhere that is connected to the sensor.

 

[Zaedster]

A fan thermo switch completes a ground to activate the fan relay. Connect battery + to pin 30, ignition 12V to pin 86, the thermo switch to pin 85, and fan power to pin 87. You can have two wires coming off 85, one for the thermo switch and one for the manual toggle to ground. Don’t generally combine the sending unit and thermo switch in the same circuit to avoid interference unless the switch has trinary resistance capabilities..

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[stwilegar]

Indeed. This is how i have it sentup. Ive ordered a second sensor (inline) to solve the issue. Then i can simply, separate the two wires, each will have its own signal. Until I hear of a better solve, Ill move forward with this plan.
Thanks!

 

[Zaedster]

Yeah, you can't share signals like that. I guess you could but the sending unit isn't a on-off switch. You'd have to wire a diode in so it cant back feed.

 

[stwilegar]

Clearly, you have a lot more knowledge on the subject than I. Thanks for sharing. I am going to research the idea of a diode installatiin just for the sake of learning.