1972-horn relay and temp gauge

[RodsnRides]

Hi folks -

I think my recent acquisition needs a horn relay. The little unit under the hood near the master cylinder "clicks" but I get no tone. I looked at Corvette Central ($20) and Eckler's ($70) but the Eckler's one looks more like mine. Mine also has a stud for a wiring terminal feed-3 wires are on it. Any thoughts?

Regarding the temp gauge. When cold, the needle is just below the 100 deg. mark. When warm, it is just over the 100 deg. mark. It doesn't even get halfway towards the center (210 deg.) mark. Is this probably just the sending unit? The heater blows warm air, and there is a 180 deg. thermostat.

Also, I assume the sending unit is on the driver's side head, green wire between #1 and #3 spark plugs. Correct? But I also see a wire going to something on the passenger side head between #6 and #8 spark plugs. This is a smaller green wire that goes to a blue wire (black GM terminal) that's in the starter harness behind the head, back of the block. What is this? I can't tell if it's a sender unless I take the ignition shielding off. The shielding does have an intentional circle shaped hole cast into it to allow this wire to pass through. Thanks in advance for your input.

Rick

 

[Vettehead Mikey]

Without testing, how can you determine it's the relay and not the horn or wiring? A simple VOM or test light would confirm whether it's faulty or not.

For your temp gauge, disconnect the wire from the sender. It's the green wire on the left side of the block. The gauge should drop to zero/full cold. Then touch the wire (briefly) to the block while some one else watches the gauge. If it deflects to full hot, then your gauge and wiring is OK and it's the sender.

 

[RodsnRides]

Fair enough on the horn relay. I can hear it click every time I press the horn button, but have not yet checked for juice at the horn or used a battery to test the horn separately from the system-that comes tomorrow.

Thanks for the sender advice. Any idea what the passenger side wire is? Car does not have A/C. This (small green 14 AWG or so) wire comes out of the head wraps around a bit, then goes to a black plastic typical GM straight connector that is a larger (12 AWG) blue wire, which is in part of the harness by the heater box. I just purchased a wiring diagram from Ecklers, so I'll have it for reference, anyways.

Rick

 

[Vettehead Mikey]

I don't know '72s too well, but believe it's part of the emission package used in the 71-74 time frame. The sensor activates a solenoid that limits vacuum advance to the distributor except when the car is in top gear and/or when the motor is extemely cold or extremely hot.

 

[RodsnRides]

I don't know '72s too well, but believe it's part of the emission package used in the 71-74 time frame. The sensor activates a solenoid that limits vacuum advance to the distributor except when the car is in top gear and/or when the motor is extemely cold or extremely hot.

Thanks, Mike
Okay. I'm normally used to the vacuum advance switch on the choke side of the intake-Chevelles had that top gear advance switch also. Now that I think of it, it was a blue wire feed from the auto tranny as well-in a two-wire plug to the advance switch. Interesting the take on the Corvette (using water temp) - but there is no interruption in the vacuum feed from the carb to the distributor. I guess someone removed that part of the equation. No worries here-I would too.

Rick

 

[Robin7TFour]

Rick, don't be suprised if you find more things rmoved ! most cars have been butchered in 30+ years

Robin