Weird 76 electrical issue - headlights on engine won't turn off/speedo light braking

[dg567]

Trying to tackle these two issues -

If the headlights are on and I turn the key off the car continues to run. If I shut the headlights, the car then turns off.

Second issue, speedo light dies when brakes are applied.


Seems like something is switched on the back of the headlight switch, but checked the connections and they seem correct.

Any help would be much appreciated!

[wrxnofx]

Did the car always behave like this? If no, what changed? If yes, have you verified the wiring into the fuse box is correct? Also, my '87 has 3 sockets under the driver's side of the dash that harnesses plug into. Perhaps two of the harnesses are plugged into the wrong sockets. Like the turn signal switch (which has wires going into the back of the headlight switch) and the ignition switch or something.

[targa80]

Originally Posted by wrxnofx

Did the car always behave like this? If no, what changed? If yes, have you verified the wiring into the fuse box is correct? .

I agree you will need to provide more of a history on the issue you are having. did the issue just start one day or have you had work done to the car? did you just buy the car and discover the issue?

taking your electrical issues one at a time would make things less complicated i.e. car keeps running with key turned off and the headlights left on.
Does your car normally turn off when the headlights are not on and you turn the key to off?

[dg567]

Car has always behaved like this - picked it up a few months back but am just getting around to working out all the issues. Replaced my turn signal switch which wasn't working correctly and properly plugged it into the headlight switch.

Another weird thing I just noticed - if the key is off or on position 1, and if my headlight switch is either in position 1 (parking lights on) or position 2 (headlights) and I touch the brakes I hear a clicking sound, and my fuel gauge jumps to half, temp gauge jumps, pressure gauge jumps to five.

[dg567]

Originally Posted by targa80

I agree you will need to provide more of a history on the issue you are having. did the issue just start one day or have you had work done to the car? did you just buy the car and discover the issue?

taking your electrical issues one at a time would make things less complicated i.e. car keeps running with key turned off and the headlights left on.
Does your car normally turn off when the headlights are not on and you turn the key to off?

Yes, Pat, car turns off like it should when the key is turned off and the headlights are off.

[targa80]

Originally Posted by dg567

Yes, Pat, car turns off like it should when the key is turned off and the headlights are off.

Now that we know this is an issue that was before your time with the car the problem could be a tech error (miss-wire) or a failure of a component in the circuit.

If you know how to use a multi-meter and can read a schematic you can do the following:
A good starting point would be to disconnect the battery and access both the headlight switch and the ignition switch. Removing the headlight switch and the ignition switch from the dash will allow you to do a visual for burnt wires and a (Resistance)continuity check with an ohmmeter between the wiring of both switches and the schematics for your model year. Verifying that the wiring between both switches is correct. If all is correct then do a continuity test between contacts of both switches looking for a low resistance (short) between terminals where there should be a high resistance (open) reading.

[rattlsnak]

IF the car will shut off when you press the brakes, (turn key off, car still running, step on brakes and car shuts off) the diode behind the speedo is burnt out. The ground is backfeeding through the brake circuit. Actually a pretty common issue.

[DRACO A5OG]

Whoa, that is nutz

[Casey at Pelican Parts]

Grounds would be a good place to start checking, I think there is also a diode for the alternator light that will cause the run on issue...

This is going to be a feather in your cap when you figure it out!!

[dg567]

Originally Posted by rattlsnak

IF the car will shut off when you press the brakes, (turn key off, car still running, step on brakes and car shuts off) the diode behind the speedo is burnt out. The ground is backfeeding through the brake circuit. Actually a pretty common issue.

Intersting...

So after some more fiddling around - it's brake related. When the brake is depressed and the headlights are on it won't shut off. If I take my foot of the brake it shuts down.

Which diod are you talking about? Any pictures of its location?

[Casey at Pelican Parts]

Originally Posted by dg567

Intersting...

So after some more fiddling around - it's brake related. When the brake is depressed and the headlights are on it won't shut off. If I take my foot of the brake it shuts down.

Which diod are you talking about? Any pictures of its location?

Here is a link for the DIODE

The old one looks like this: CLICK HERE

The new ones look like this:

[rattlsnak]

Technically you don't have to remove the old one as it is basically acting like a normal piece of wire, but you can remove the speedo and install the new one in line with the blue wire from the Alt feed before the 'charging bulb' on the top of the speedo and it should fix it.

Look at this thread. I think it has a schematic..

3.2 will not turn-off

[dg567]

Originally Posted by rattlsnak

Technically you don't have to remove the old one as it is basically acting like a normal piece of wire, but you can remove the speedo and install the new one in line with the blue wire from the Alt feed before the 'charging bulb' on the top of the speedo and it should fix it.

Look at this thread. I think it has a schematic..

3.2 will not turn-off

Seems as though mine won't shut off when the brake is applied and the key is turned off. You're seemed to shut off when the brake was applied.

[rattlsnak]

headlights on or off?

[dg567]

With headlights or parking lights on this occurs...

[rattlsnak]

ok, then should be the same fix. Yours is just feeding back through the light circuit instead of brake circuit. Take out your speedo, or any gauge, and run a jumper wire to ground and start car, turn lights on, turn key off and then touch it to ground and if it cuts off then, same thing issue and the diode will fix it.

[dg567]

I have a new diode coming Monday - can't find the one behind the gauges though?

[rattlsnak]

I have looked on 3-4 different cars before and have never found it. You dont have to remove it as it is acting like a straight piece of wire now anyway. No harm.