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Try pulling the wire off the sender. How does the gage respond? Short the wire to to a good ground. Again how does the gage respond?
 

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Opening or shorting the sender wire should drive the gage around. If that's not happening, check the ground on the gage, the power wire on the gage, and try shorting the sender wire right at the gage. If nothing shows up, the gage has a problem.
 

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The tan wire #31 connects to the pressure sender and nothing else. It should have 12+ V (tan wire to ground) at the sender with the ignition on and the wire disconnected from the sender.
 

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Discussion Starter · #8 ·
Well guys this is getting pretty complicated, but I will try and give you the whole story. My car has idiot lights and I want to convert to GM factory gages. I went to a junk yard and purchased the whole dash housing because the gages plug into metal sockets that aren't on the idiot light housing and the PCB is different. I have a GM service manual and the wiring diagram shows that the wire from the new sender for oil pressure connects to wire 31. I therefore spliced into tan wire 31 and connected the other end to the new sender. The diagram also shows that a new wire 931 should run from the PCB connector to the original oil pressure sender on the intake to the electric choke feed circuit 78 which is a light blue wire. This is where I think the gage gets it's 12v source. With the idiot lights 31 gets it's power from circuit 39. I did check 31 with the ignition on and with the motor running and found .8v. I thought I should see 12v with the motor running because the original sender should have closed, but I didn't. To muddy the waters even more the 1st time I ran the motor I got a check "choke" lamp and then check engine light. The trouble code is 24 which is for the vehicle speed sensor circuit. I'm not sure how that code is related to the gages. I think I have the "can't see the forest for the trees" syndrome. Thanks for all who are trying to help with this.
 

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I wasn't able to find a copy of the 85 diagram, I got one for 83 and one for 87 so on some things I can't give exact information.

Yes wire 31 connects to the new sender and should have no other connections. It gets power from the gauge. The gauge has three connections, one is power from #39, one is ground from #150, one connects to #31. If 31 is a complete circuit to the new pressure sender and if the pressure sender is grounded to the engine, the gauge should work. With the tan wire disconnected from the sender the circuit is open and no current is flowing so if the circuit is correct you will measure 12+ volts on the tan wire (ignition on). If you don't have power go back to the gauge checking connections in the tan wire #31 until you find where you're loosing power. If you don't have power at the gauge it may be a bad connection to the gauge or a bad gauge.

I think your gauge cluster has a CHOKE indicating light, it gets power from #39 and is connected to the choke heater by #931 (I believe this is the power for the choke heater) The light blue wire goes to the old oil switch. When the engine is not running the oil switch is closed, with the ignition on the CHOKE light will be on and the choke heater will heat. When the oil pressure increases the switch opens, CHOKE light and heater re off. I can't be sure of this because I don't have the 85 diagrams.
NOTE: This wiring should not connect to the tan wire #31.

On your 85 the cruse control speed pickup is on the back of the speedometer If the pickup is not connected or the speedo cable is not connected the code 24 will be in. I don't know what years had the speed pickup on the speedo. An older cluster may not have the pickup.

Did you add a resister wire from the Ignition switch to circuit #25. This is for the alternator. The light cluster had a light that feeds power to the alternator for initial excitation and GEN indicating light. The gauge cluster has no connection at the cluster to #25 so a 10 ohm resister wire (brown/white) was included in the wiring for a gauge dash.
 
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