'68 Dash Warning Lights

Cougar Community Classic Cougar Maintenance Restoration and Repair
1

OK, so in a standard (non-XR7) '68 dash I should have warning/indicator lights for high beam, oil pressure, charging system and brakes - correct?

Should any of these come on as a check if you have the ignition key in the ‘start’ position but the motor not running? If not, how are you meant to tell if the relevant systems and bulbs are working properly?

The previous owner of my car had an oil pressure gauge installed and the sender unit would have been changed, so I don’t expect the oil pressure check light to work. High beam is easy enough to test, but what about the others? And does anyone know what the brake warning light is meant to signify - that the park brake is on or something else?

BTW, I don’t currently have an owner’s manual but am working on acquiring one!

2

The amp and normally the oil pressure light will come on with the key in the on position, in the start position the Brake system pressure light will come on and then go off in the run position. The brake light is for system pressure and will come if you lose pressure in the front or rear brakes thus setting off the proportioning valve that turns on the light. The parking brake light was an option and was located on the lower left side of the dash above the release handle. You should also have a Seat Belt reminder light, just under the right turn indicator light. It to will come on with the key on for 3-5 seconds.

3

Actually the BRAKE warning lamp has nothing to do with a proportioning valve. The BRAKE warning lamp comes on if the differential pressure switch in the brake distribution block is moved from center.

Four wheel drum brake equipped Cougars don’t even have a brake proportioning valve.


4

Hmm, none of mine light up in any key position as far as I can remember so this needs some further investigation. Do you happen to know what the trigger condition is for the amps warning light to come on during driving?

I’ve downloaded the electrical system diagrams from WCCC and the only mention I can find of a seat belt reminder light is for the overhead console on XR-7s. Are you 100% sure this should be on a standard '68 dash as well?

5

OK, did some more digging through the Cougar electrical wiring diagrams. From what I can make out the situation should be as follows:

Amps light - should be ON with ignition in RUN position and engine not started, otherwise OFF if no problem

Oil pressure light - should be ON with ignition in RUN position and engine not started, otherwise OFF if no problem

Brakes light - should be OFF in all situations unless there is a problem

So by the above logic, if you turn the key to the RUN position but don’t start the engine, the Amps and Oil pressure lights should be illuminated but the Brakes light will not. On one Mustang forum I noticed someone said they thought the brakes light may come on as a test with the ignition in the crank position but there wasn’t much in the way of supporting comments.

If anyone could take the time to confirm all the above before I rip my dash cluster out I would be most grateful!

On the seat belts reminder, there does indeed seem to be a lens for that function where Richard said, but with my car there is no bulb or wiring behind it so I imagine that might have been an option on the base model Cougars?

6

Per the 68 owners manual:

Seat Belt reminder comes on for a few seconds when the key is in the Run position.

Brakes Warning light comes on when the key is in the Start position. Off otherwise unless failure detected.

7

I believe that the seatbelt warning light came with the optional deluxe seatbelt package, but was not standard equipment in '68.

8

Is there a difference between a Seat Belt reminder light that stays on for a few seconds and a light that stays on until the deluxe seat belts are latched? The owners manual implies that the reminder light was a standard feature and the base dashes all have the spot.

9

There is no seat belt light available in the '67 - 68 Cougar that has anything to do with anything latching. Any of them operate strictly on a timer. It is a seat belt reminder light.



10

My standard dash has the lens and bulb socket for the seat belt reminder, but no wiring or relay.


To help with troubleshooting this, does anyone know if the pressure differential switch in the brake system is normally open or closed?

11

When pressure is out of whack, the switch contacts ground. The bulb lights up when voltage from switch is compared to ACC or RUN-only lines, depending upon year/model of Fords.

12

OK, I’ve been completely through the dash cluster and checked that all bulbs are good and wiring intact. Have confirmed the BRAKES light does come on while cranking the starter and goes off again once the engine is running.

However, I can’t get either the OIL or AMPS lights to come on at any stage. I’ve looked through my newly acquired owner’s manual and it doesn’t make mention of either of these lamps coming on with the key in either the acc or run position as a bulb test. The only reason I believe that may be significant is the manual explicitly highlights the BRAKES light will come on as a test when the key is in the start position.

Does anyone else’s experience line up with mine or do I need to do some more investigating?

13

I think the seat belt reminder was standard as you say. You are probably missing the relay.

The DP switch is normally open when centered in the distribution block. It provides a ground for the lamp when moved forward or rearward.


14

If you now have an oil pressure gauge then the OIL light circuit is not connected so the bulb will not come on in any key position. The AMP light is turned on/off from the voltage regulator. With the key ON and engine not running there is no output from the alternator so the voltage regulator turns on the AMP bulb to indicate no output. Once the engine starts and the alternator outputs the voltage regulator turns out the AMP bulb.

Look on the voltage regulator for a connection labeled ‘I’ and see if the connector has a wire at that position. If no wire then your wiring harness is for an XR7 or has been messed with. If you have a wire then the connections are corroded or VR bad.

15

Good point - I might try grounding the sensor wire just for fun to see if I can get the light to come on.


Thanks, will check it out.

16

OK, grounded the oil pressure sensor wire and the OIL warning light does indeed come on, so check that one off the list.

Still puzzling over the AMPS light. Looked through the wiring diagrams and the two wires coming off the AMPS light socket are numbered 30C and 643. Wire 30C runs back to the constant voltage unit on the back of the dash cluster, which I assume is to provide a reference 12V signal. Wire 643 runs to a connector block where it looks like it ends up spliced with wire 32, which runs between the ignition switch and the starter solenoid ‘s’ terminal.

So by my reading, neither of these wires is connected to the voltage regulator which would make it impossible for the lamp to light when there is no output from the alternator. Obviously I’ve missed something or just plain read the diagram wrong, but which is it?

17

You’ve mis-read the electrical schematics or the schematics are incorrect. One side goes to the voltage regulator/alternator and the other side has a resistance wire and a connection to either ACC or to a RUN-only line.

18

It’s the second option - the #$%@ schematics are incorrect!

Specifically here:

In the area circled in pink, wires 904 and 643 have been transposed. This now makes sense: 643 comes from one side of the AMPS bulb to the connector marked ‘E’ above. On the other side of the connector, it should become 904 which runs down to the ‘I’ terminal on the voltage regulator, NOT pick up wire 32 which runs to the starter solenoid.

Once I figured this out, it was a simple matter to ground out the wire at the regulator terminal and sure enough the AMPS light came on with the key in the run position. Checked the ‘I’ terminal on the regulator and it doesn’t complete the circuit to ground under any condition so I’m starting to suspect it may be faulty. It does charge the battery OK but there’s some weird behaviour where it doesn’t charge properly if I leave the ‘I’ terminal disconnected which is not what should be happening if I understand correctly.

19

The alternator light is a two wire light, with neither the housing nor base is grounded. One of the two wires on a two wire light is powered via the ignition switch in the ON position with the other wire connects to the “I” terminal on the regulator. This flows through to the field of the alternator, the windings of which finally go to the negative ground.

When the engine is not running and the ignition switch ON, the alternator provides the ground, thus the alternator light glows since the power is provided via the ignition switch. When the engine starts, the alternator stator terminal supplies the positive voltage to the “S” terminal, which closes the field relay in the regulator and now the “I” terminal becomes positive. With both wires going to the plug being positive, the light goes out.

Remove the regulator and make sure that the bolts and the underneath area of the regulator that contacts the fender apron is clean. Also make sure the ground wire at the alternator is clean and tight.

To test your charging system while on the car,

At the Voltage regulator, the plug is vertical with the following 4 wires in the connector from the bottom to the top:
I - bottom goes to the ignition switch (904 green-red ) and the dash indicator light circuit (643 yellow-black). Note the 904 circuit is hot only when the ignition is ON or ACC position.
A - This wire goes to the Bat post at the alternator ( circuit 152 - yellow ) . If the battery is connected, you should be able to measure 12 V here. This is used as a voltage sensing wire. Note wiring diagram shows that this wire goes directly to the battery.
S - Stator output from the alternator ( circuit 4 - white-black stripe). Stator output is a 1/3 ac unrectified wave output from the alternator. This can be used for the electric choke but this terminal will only have roughly 8.3 Volts.
F - Field - This is the field excitation circuit to the alternator. ( circuit 35 - white )

To test the alternator, you need to excite the circuit by revving the engine above 2000 rpm. Turn on the headlights, stereo and heater blower to place a load on the electrical systems. Next measure the voltage at the Bat post on the back of the alternator or at the starter solenoid Battery terminal. This should measure between 13.5 and 14.5 volts.

If the system reads only 12 V, basically battery voltage, then disconnect the plug at the voltage regulator. Using a jumper wire with male connectors on both ends, place one end in the F terminal connector and the other end on the A connector. This effectively bypasses the voltage regulator and provides full excitation to the alternator. The voltage reading at the bat post should now read 15V. If it still reads only 12 V, then the wires to/from the alternator and the regulator are suspect.


Let me know if you need any additional information

Coach Jack


References:
http://www.jalopyjournal.com/forum/threads/gm-10si-3-wire-alternator-question.217154/
http://www.mercurycougar.net/forums/archive/index.php/t-15503.html
http://www.allfordmustangs.com/forums/attachments/classic-tech/164262d1348605883-1967-mustang-289-tach-install-how-install-tach-67-68-mustang.pdf

20

Hi Coach Jack, many thanks for your comprehensive reply. You’ve taught me at least two things I didn’t know:

  • there is a path through the regulator from the ‘I’ terminal to the ‘F’ terminal to complete the circuit to ground when the alternator isn’t running
  • 12V is required to the ‘I’ terminal for the alternator to start working on Fords with a charge indicator light

With the first point and looking at the diagram you linked to on allfordmustangs.com:

there should be a little over 10 Ohms resistance between the ‘I’ and ‘F’ terminals on the regulator, correct?


On the second point, all the stuff I read said the ‘I’ terminal could be left disconnected if desired without any problems, but the other reference material you provided (and the way my regulator operates) says on Fords with a charge indicator light it must be connected to excite the alternator.

I’ll try the tests you suggested and see if I can get a connection to ground through the alternator ‘F’ terminal and report back.