66 Parking Brake Warning Light

[Leo M.]

Having a problem with the parking brake warning light on my 66. I've changed the 257 bulb (ugh!!!) and installed a new switch at the bottom of the parking brake shaft. When I turn the key on, the fuse for this unit fails. Other gauges that could be on this circuit such as fuel and temperature are working, although the temperature gauge is reading low I suspect due to a new sending unit that I obtained from one of the Corvette supply houses. Any thoughts or suggestions would be appreciated.

[Stephen L.]

Re: 66 Parking Brake Warning Light

Sounds like you have a short in that circuit. You should obtain a wiring diagram of your car and trace out what all is on that circuit.
In my 67 that circuit feeds the gas gauge, the e-brake light, the temp gauge, and the fuel tank sender. (I suspect the circuitry would be the same for 1966) I would disconnect the temp sender, and the fuel tank sender, then install a new fuse. If the fuse blows you have a short in the associated wiring. If the fuse holds then reconnect the items, one at a time to see which one is faulty. The fuel sender and the fuel gauge as well as the temp gauge are connected directly to the fuse in question. Good luck

[Richard M.]

Re: 66 Parking Brake Warning Light

When the fuse blows, is it when the E Brake is applied, or not?

The 257 bulb gets constant(key on) power from Pink, but is switched on via the ground path through the E brake switch.

If the fuse is fine before applying the E brake, based on the fact you're saying the Fuel and Temp gauges are operational, then my suspicion would be a short between the Pink power wire and the Tan ground wire(from E brake switch)....... in the 257 bulb socket.

This could be checked by removing the Tan wire from the E brake switch and use a Ohmmeter between Tan and known good cluster Ground. You would normally read low ohms through the bulb filament when cold/unpowered and you could get a baseline reading from a know good 257 bulb separately. A dead short reading, say 0.1 ohms or so(plus meter lead error), would tell me the bulb socket is shorted.

Rich
edit... wiring diagram below. Note also the Pink goes to the Neutral Safety switch if Auto transmission, and also to Backup Lamp Switch if equipped.

[Leo M.]

Re: 66 Parking Brake Warning Light

Had some time today and eliminated the temperature and fuel sending unit as the cause. Also the fuse pops whether the parking brake is engaged or not.

[Richard M.]

Re: 66 Parking Brake Warning Light

Had some time today and eliminated the temperature and fuel sending unit as the cause. Also the fuse pops whether the parking brake is engaged or not.

Leo, Okay, I would remove the Tan wire from the switch then check again.

Does your car have Backup Lamps? Is it a Auto trans?

Rich

In the throat of the secondary there is a signal orifice I would presume for supplemental / maximum vacuum signal for the diaphragm. I check diaphragm operation by holding my pinky over the orifice and using the mity vac on the rubber vac line.

Chris, I believe you replied to the wrong thread.

[Leo M.]

Re: 66 Parking Brake Warning Light

Will remove the tan wire and try again. It is a 4 speed and does have back up lights which are not working. I have a new back up light switch but the lights still do not work. I recently replaced both the tele column wire switch and the engine compartment wiring harness. The back up light problem and the parking alarm problem existed before replacing either of the wire harnesses.

[Richard M.]

Re: 66 Parking Brake Warning Light

Will remove the tan wire and try again. It is a 4 speed and does have back up lights which are not working. I have a new back up light switch but the lights still do not work. I recently replaced both the tele column wire switch and the engine compartment wiring harness. The back up light problem and the parking alarm problem existed before replacing either of the wire harnesses.

The BU Lamp wiring is fed from a 2 terminal connector in the engine bay, which is fed from the Pink wire in the Main harness which also feeds the other items in the path we talked about.

In the Engine Bay, at the firewall near the area of the Ballast Resistor is where this 2 terminal connector resides. It comes out of the cabin in the same large grommet where the Ignition and Wiper Motor wiring exits. The Pink is the feed and the green is to power the BU lamps, via the Rear Harness in the cabin.

If the BU Lamp switch harness is still attached to this connector, remove it and test again. But I'm confused why the Fuel and Temp gauges work when the key is on, yet the fuse blows. Maybe I missed something.

Eventually after getting this problem sorted out, to test the BU Lamps, you can simply short the Pink and Green wire terminals in the connector to bypass the BU Lamp switch. Remember though key to IGN for this to work.

Rich

[Don H.]

Re: 66 Parking Brake Warning Light

Originally Posted by Chris Hewitt (33863)
In the throat of the secondary there is a signal orifice I would presume for supplemental / maximum vacuum signal for the diaphragm. I check diaphragm operation by holding my pinky over the orifice and using the mity vac on the rubber vac line.




Chris, I believe you replied to the wrong thread.

I moved his post to your thread which is where I think he meant it to be.

[Chris H.]

Re: 66 Parking Brake Warning Light

Thanks Don, fat fingering on my phone.

[Leo M.]

Re: 66 Parking Brake Warning Light

Removed the tan wire to the parking brake - fuse still popped. Jumpered the back up light socket and no back up lights.

[Leo M.]

Re: 66 Parking Brake Warning Light

Might have isolated the problem. Unplugged the rear wire harness from the main harness. Fuse held and parking brake warning light flashed as it should. Will look for issues along rear harness. Any advice or suggestions are appreciated.

[Richard M.]

Re: 66 Parking Brake Warning Light

Might have isolated the problem. Unplugged the rear wire harness from the main harness. Fuse held and parking brake warning light flashed as it should. Will look for issues along rear harness. Any advice or suggestions are appreciated.

Leo, You may get the same result if you unplug JUST the BU switch plug at the firewall. The rear harness has the BU lamp feed from the BU switch, which resides in the Body Connector you disconnected.

I'd start by removing both BU lamp bulbs and check the bulb sockets for a short to ground.

The Pink feed to the Fuel sender is also in this Rear harness. I'm wondering if there is a internal harness short between the Pink to the sender and the BU lamp circuit.

You may need to get behind the BU lamp housings and harness wiring for a closer look. If your spare tire tub is there and you have undercar exhaust, it may be tricky to see up there. The harness sockets for the Tail and BU lamps can be removed from their housing metal sockets. The round connectors have tabs(careful, very delicate), and they lock into the sockets, and stay tensioned when a bulb is installed. Make sure you have the correct bulbs in there. a single terminal tipped lamp. I forget the bulb #. Also note that the bulb socket in the housing is specially designed to take the proper bulb. A dual filament tail lamp bulb has offset ground lock tabs. The BU single terminal tip bulb has tabs that are equally offset. BU lamp housings have special metal sockets with the equally offset tab receptacles. Sorry no detail pics. Sometimes prior folks may upgrade to BU lamps and don't change the inner tail lamp housing sockets to the proper BU lamp type. If yours are like that it could be part of the problem on non working BU lamps. I had one like that once. But IIRC, all 1966's should have BU lamps.

Here are some photos from a '66 rear harness(new) as it traverses horizontally along the rear fascia panel. The Green wires are for the BU lamps.



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[Leo M.]

Re: 66 Parking Brake Warning Light

Thanks Richard. I have the BU switch from the transmission to the connector on the firewall disconnected but if there was a short or ground in the wires from the BU lights in the rear harness I'm thinking it would still show up. I did take the rear valance off and check all the lighting wire connections and again disconnected the lines from the tank sending unit. I did find an untaped splice in the black ground wire however unfortunately that was not the problem. I will check the BU bulbs and bulb sockets. Up until I acquired this car a few months back it had pretty much been sitting for the last 29 years. Thanks for the tip on the BU bulbs and sockets. As luck would have it I am bringing the car to the NW Regional this coming weekend for flight judging and would love to have the back up lights and parking brake warning light operational.

[Richard M.]

Re: 66 Parking Brake Warning Light

Thanks Richard. I have the BU switch from the transmission to the connector on the firewall disconnected but if there was a short or ground in the wires from the BU lights in the rear harness I'm thinking it would still show up. I did take the rear valance off and check all the lighting wire connections and again disconnected the lines from the tank sending unit. I did find an untaped splice in the black ground wire however unfortunately that was not the problem. I will check the BU bulbs and bulb sockets. Up until I acquired this car a few months back it had pretty much been sitting for the last 29 years. Thanks for the tip on the BU bulbs and sockets. As luck would have it I am bringing the car to the NW Regional this coming weekend for flight judging and would love to have the back up lights and parking brake warning light operational.

Leo, You definitely want to fix any electrical issues before Operations Checks. Big hits for stuff like that.

Rich

[Leo M.]

Re: 66 Parking Brake Warning Light

Ok so I finally have had some time to get back to this problem. Given that the fuse did not blow and the emergency brake warning light operated when I disconnected the rear wire harness I thought I had isolated the problem with that harness. I checked the rear harness and connections, as well as the back up light bulbs and found nothing. As a result I installed a new rear harness. The bad news is I still have the same problem. Turn the key on and the top left fuse for the emergency brake warning and back up lights pops. I disconnected the pink wire at the fuel sending unit and the fuse does not pop. Could the fuel tank sending unit be my problem or is the fuse holding just because there is an open circuit?