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71 Ss idiot light to gauge conversion

1962 Views 6 Replies 3 Participants Last post by  Steve S
I am trying to follow the instructions for conveting a dash wiring harness in a 71 SS that currently has idiot light SS gauge cluster to work with tach and gauges. The only problem I am having is the the amp gauge. I have added one wire from gauge cluster connector pin 4 (generator/ammeter) to the bulk head connector. The problem is gauge cluster Pin 3, the instruction say nothing about this wire like it already exists. It does but it seems to me that you have to move the wire in the bulkhead connector. I am using the diagrams from this link. http://members.home/jimmy4/conversion.htm

Steve Strasemeier (70SS 396, Fathom Blue/White Stripes)
My 70SS
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The wire in #3 position, on your idiot light harness, should be brown, it connects at the bulkhead to a brown/white wire. You can clip the brown wire. You must leave the brown/white wire. It connects to the ignition switch and to the voltage regulator, it is a resistor wire and is needed for proper operation of the alternator. The brown wire was for the alternator idiot light. You will need a new wire (or use the brown wire) in the #3 position, it will connect to the bulkhead at location *T D, from there it will connect to the horn relay. The wire in #4 position will connect to the bulkhead at location *S D, from there it will connect to the “Junction Block“ located to the right of the radiator, near the battery (main power feed from the battery). You should use a #20 fuseable link on both under hood connections for the amp gauge, available at NAPA. The factory used a black/white/dark blue wire for the #3 and a black wire for #4, both #16 wire.

* The bulkhead connector is marked with columns A B C & D and rows S T U V W X Y & Z.

The Amp gauge does not carry current. It is a volt meter scaled in amps. It measures the voltage drop from the "Junction Block" to the horn relay (on the factory harness the #4 wire, black\white\dkblu is connected to a soldered junction between the alternator and the horn relay) .5 volt drop is aprox = 40 amps.
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The resister across the vertical terminals should be orange, 86 ohms. I have one 70 temp gauge that has a 91 ohm. The sensor resistance vs. temp is as follows (I have only one to test) 80 F = 710 ohms, 100 F = 545 ohms, 125 F = 400 ohms, 170 F = 260 ohms, 210 F = 200 ohms. The relationship is not linear. If I get a chance I’ll test the sensor at work. If I get significantly different results I’ll post them.
Here are revised Resistance VS temperature values.

80 F = 700 ohms, 100 F = 555 ohms, 120 F = 455 ohms, 140 F = 370 ohms, 160 F = 300 ohms, 180 F = 245 ohms, 200 F = 205 ohms, 220 F = 175 ohms, 240 F = 150 ohms, 260 F = 130 ohms, 280 F = 115 ohms, 300 F = 105 ohms.
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