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Getting ready to start the re-wire of my 67 Bird. All new harnesses. Since I'll be using gauges that have built in warning lights for oil pressure and water temp the stock wires for the original sensors won't be used. Looking at the wiring diagrams it appears that the sensors were a ground source for the factory warning lights. If this is true wouldn't those have a 12 volt ign/keyed source I could use as a trigger for a relay??
 

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Not really. The way the temperature light works is the keyed voltage goes to the bulb, the other side of the bulb goes to the sensor. At a predetermined temp the sensor grounds, lighting the bulb. So from those wires you get the voltage minus the resistance of the bulb.

If you have upgraded to an alternator with internal regulator there might be a keyed 12 volt available there but at least one of those goes thru a bulb also. The only other keyed source that I can think of is distributor feed and that is resistored down also.

Maybe just replace the temperature bulb with a paper clip? :smile2:

Jeff
 

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There’s keyed 12v at the wiper motor. Should be fine to trigger a relay.
 
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OP

IDK if you are talking about a stock or aftermarket (AAW??) wiring harness but either way I would run a wire through a firewall grommet from the IGN circuit of under dash fuse block. That is what I did for my gauge sender install.
 

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Discussion Starter #5
Not really. The way the temperature light works is the keyed voltage goes to the bulb, the other side of the bulb goes to the sensor. At a predetermined temp the sensor grounds, lighting the bulb. So from those wires you get the voltage minus the resistance of the bulb.

If you have upgraded to an alternator with internal regulator there might be a keyed 12 volt available there but at least one of those goes thru a bulb also. The only other keyed source that I can think of is distributor feed and that is resistored down also.

Maybe just replace the temperature bulb with a paper clip? :smile2:

Jeff
I just found this out also. Thanks.
 

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Discussion Starter #6
OP

IDK if you are talking about a stock or aftermarket (AAW??) wiring harness but either way I would run a wire through a firewall grommet from the IGN circuit of under dash fuse block. That is what I did for my gauge sender install.
It's an aftermarket from M&H which is identical to stock. I can either use the IGN as you suggested or I just remembered I could use the coil wire also. My plan was to use a junction block I got from MAD Electrical, feed power to it through a relay with full battery power anyway. So the coil can be feed from the junction block also. Looks like I may have two alternatives now.
 

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It's an aftermarket from M&H which is identical to stock. I can either use the IGN as you suggested or I just remembered I could use the coil wire also. .
If you are referring to the "white" wire that goes to + coil...that is a resistance wire on a stock wiring harness which knocks down the VDC to around 8 vdc. If you are running a points distributor that is what you want but a HEI you need to either cut that wire at the firewall block and splice a regular copper wire or just run a new copper wire from IGN to the + coil
 

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Discussion Starter #8
If you are referring to the "white" wire that goes to + coil...that is a resistance wire on a stock wiring harness which knocks down the VDC to around 8 vdc. If you are running a points distributor that is what you want but a HEI you need to either cut that wire at the firewall block and splice a regular copper wire or just run a new copper wire from IGN to the + coil
I knew there was some resistance in the wire but thought it was near the end. Not sure 8 volts is good enough for a relay work properly. Guess I'll play it safe and run a lead from the IGN tab on the fuse box.
 

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