strange electrical issue...

[coppertop666]

65 Monza

Last week a buddy of mine noticed the left rear brake light wasnt working BUT the left rear turn signal did. Today I took a look to see what exactly is happening and here is the issue.

running lights / taillights all work normally

Brake light works on the right side only

right turn signal works both front and rear lights

left turn signal works on the front but only SOMETIMES on the left rear.

When I first try the left turn signal it works for a few seconds then turns off while the dash indicator and front light still work normally. I then turn off the left turn signal, turn it back on again and it works for a few seconds then off again (still no left brake light no matter what I do). First thought was maybe I had a bad bulb or corrosion causing an intermittent issue, changed bulb and checked socket, same issue.

I checked the multi connector by the firewall with a test light and got the exact same symptoms. I then checked the multi connector under the dash, same thing...

Any clue where I should start looking next?

On another note my fuel gauge works intermittently too. an example is when I fill the tank, sometimes it will show full and others it will show only 1/4 tank. Then lets say I have 1/2 tank, sometimes it will show 1/2 and others it will show 1/8. Can this be related possibly? Bad ground somewhere?

Any info would be appreciated

[91blaze]

Make sure all the screws are in the bottom of the instrument panel. If you look you can see there is one that grounds the entire panel. As for the brake lights, most likely that would be in your turn signal switch. Sometimes the contacts get corroded, bent, or loose and can cause headaches. Mine did something similar and I found that a contact had been bent so it didn't touch where it should.

[coppertop666]

Thanks blaze - will check the dash/signal switch and report back!

[bbodie52]

The left rear brake lamp and turn signal filament, socket, ground, wiring harness (from the turn signal switch to the bulb socket) are the same. The only thing that changes (within the turn signal switch) is the power source for the bulb. Moving the turn signal lever switches the power source from the brake pedal switch to the flasher. The same action also adds the front turn signal bulb on the same side to the circuit, so that both the front and rear bulb filaments are powered by the flasher at the same time.

The power feed for the left front turn signal and the left instrument panel turn signal indicator bulb are spliced together at the 12-pin multi-connector, so as long as power is fed to the front bulb the instrument panel indicator will receive power too. The left-rear circuit is separate from the left front in the harness, so the intermittent left rear flashing would not be reflected at the instrument panel. A damaged or corroded contact within the turn signal switch would likely be the cause of your intermittent left rear turn signal and the failed left brake lamp. The connection at the curved multi-connector on the steering column could also be intermittent or faulty. Since the left rear brake consistently does not work, but the left rear turn signal works intermittently, this would likely indicate a good circuit from the turn signal switch all the way back to the bulb. You could confirm this by temporarily applying 12 VDC to the 20 B/Y (20 gauge BLACK with YELLOW STRIPE) wire at the curved multi-connector at the steering column. The application of voltage at that point should consistently illuminate the left turn signal/brake lamp filament. A successful test of this type would likely indicate intermittent power from the turn signal switch. You could also use a test lamp or multimeter to check for voltage at this connector from the turn signal switch when the brake pedal or the left turn signal is activated. The bad contact is likely within the turn signal switch itself. If both segments of the circuit test OK, the fault may be in the curved connector itself when the two halves are connected together.

This pic is from my 66 Corsa with the turn signal switch inside the column opened up.

[coppertop666]

Thanks again for the detailed post Brad - just to clarify, the left rear brake does not work only the right side; the left turn signal does work but intermittently - do you (like 91blaze) think the issue still lies in the turn signal switch? I was just under the dash and noticed that the ground strap is a little corroded so I am going to clean it up and put a star washer like someone else suggested in a different post. After that I think I am going to remove the steering wheel and check out the switch - will update later

[66vairguy]

The LM gas gauge problem can sometimes be a bad dash ground. It's a known problem that the LM dash ground is problematic. I run a separate ground wire on my cars. The other ground issue is the wiper switch. The dash area the wiper switch grounds to (wipers work by grounding the "hot" motor leads at the wiper switch) can become rusty. A typical fix is to attach a ground wire to the wiper switch.

As others said - you probably have a turn signal switch problem. A common failure. If you haven't changed the turn signal switch I recommend finding someone with experience to help. Not a job for the inexperienced.

BTW - if both the brake and turn rear lamps are intermittent check the bulb socket grounds. A problem on both the EM and LM cars. Some find sockets with a ground wire on them, some add a ground wire to the socket.

[Wagon Master]

My take on your issue is your left turn signal is not cancelling all the way. Raise the lever up slightly and try the brakes.
either that or the turn signal switch has a flaky set of contacts.

[flat6_musik]

I think turn signal switch too. It's nice when you have a fresh switch installed.

[coppertop666]

Well you guys were right; turn signal switch!!!

I cleaned up the contacts an tested and it seems to be working but the contacts themselves seem very weak even after bending them to make a better connection so it looks like a new switch is in order.

Also regarding the fuel gauge, I cleaned up the ground strap and even tried the star washer but still reading 1/4 tank when i just filled it. Maybe its a loose wire or bad ground somewhere else possibly?? I also noticed that the idiot light for the cooling fan has always been dimmer than the temp/pressure light. I replaced the bulb while under there and checked the socket and its still way dimmer than the other - related possibly or am I reaching with that one???

[bbodie52]

A mechanical defect, such as a stuck tank sending unit or a frozen display in the gauge itself are both possibilities.

I would think that the first step would be to perform a fault isolation test to determine if the gauge in the instrument panel responds to an open or ground condition at the sending unit end. As you can see in the fuel gauge functional description below, the fuel gauge contains two electromagnetic coils — one on the "F" side and the other on the "E" side of the gauge. The magnetic coil on the "F" side provides a constant pull in that direction. The "E" coil is potentially stronger than the "F" coil, but its magnetic pull is variable, and based on the amount of current flowing through the variable resistor coupled to the float in the fuel tank. Minimum tank resistance (Empty) will produce maximum current flow — the equivalent of a short to Ground. This will place the "E" coil at maximum pull and will move the needle all the way to the "E" side of the gauge. Maximum tank resistance (Full) will decrease the current flow through the "E" coil in the gauge (the equivalent of an "Open" no current condition — making that side significantly weaker than the "F" coil), which will pull the in indicator on the fuel gauge all the way to the "F" side.

In other words, with the ignition key in the ON position, disconnecting the wire at the fuel tank sending unit should cause the fuel gauge needle to move all the way to the FULL mark. Conversely, shorting that wire to ground should bring the "E" coil in the gauge to maximum, which should pull the needle all the way to the EMPTY mark.

If the gauge fails to respond to these test changes, you should be able to use a multimeter to measure DC voltage between the tan disconnected sending unit wire and ground. If you measure 0 voltage there, it is likely that there is no voltage being provided to the fuel gauge, which would mean that neither electromagnetic coil in the gauge is energized — which would leave the indicator needle static and not moving in either direction. It would remain in a random position between the "F" and "E" marks.

There are only two wires at the fuel gauge. On 1964-1969 Corvairs, the 20 Gauge Tan wire (20 T) connects to the fuel tank sending unit. The other 20 Gauge Black with Pink Stripe wire (20 B/P) provides 12V DC to the gauge whenever the ignition key is on. The gauge metal housing must also be properly grounded to properly energize the "F" coil, to provide a constant magnetic pull in that direction. If voltage is fed to the gauge, you should also see voltage coming out of the gauge via the tan wire to provide voltage to the tank sending unit variable resistor.

The results of these troubleshooting techniques should point in the direction of the source of your gauge trouble.








The fuel gauge also depends on a good ground for the Monza instrument panel...






Part number C847: 65-69 STAINLESS GAS TANK SENDER UNIT ** GKT-C155,RETAINER-C156,STRAINER-C261*

Weight: 1 lbs 0 oz
Catalog Pages(s): 69(2)
Price: $ 54.85

[66vairguy]

Brad probably covered it, but if not - the float/sender at the tank has a ground wire to the body and it tends to be broken or corroded. If the sender ground is good - it's time to pull it for inspection AFTER you get most of the fuel out of the tank. Definitely an outside job.

The FAN lamp tends to be dimmer - it is activated by the alternator/regulator circuit when the fan belt comes off and the alternator stops turning. The bulb is grounded through a load so it's not a direct ground. In fact the lens in the dash cluster was actually a lighter red to compensate and with age the lens sometimes get darker.

Many install a buzzer with a timer, otherwise the buzzer goes off every time you start the car.

[coppertop666]

Thank you all for the information; when I get some more "vair" time I will update again

Matt

[coppertop666]

Quick update:

Over the weekend I replaced the turn signal switch with a new one from Clarks, all lights working perfectly now; thanks again for the help with the diagnosis!

Regarding the fuel gauge, I havent had a chance to dig in but hopefully this coming weekend I will get time and will update when I know more

[64powerglide]

When I got my 64 the gas gauge didn't work, when I pulled the sending unit out the tank had 2 inches of gunk in the bottom & the sending unit didn't have a float on it. Cleaned the tank & put in a new Clark's unit & it worked fine for one day then the gauge was all over the place. Took the sending unit out & the float had gas in it, soldered seam leaked. Called Clark's & they sent me a new float, been working fine for 2 & 1/2 years. Just a thought.