Underdash "lights not working" 68 XR7

OK this is a very regular problem we have with our new Cougars once we dive in working on them. I recently decided that while I am waiting to get painted I wanted to get my wiring dialed in before i start putting everything back together after paint. So I have read a bunch of cases before deciding i need to ask my own questions so here goes:

  1. I started at the fuse box. I checked for power on each side of each fuse. I didnt find what i expected, i had power on the top fuse and power on the right side fuse, that was it, My expectation was to
    find power at each fuse with the battery connected, YES? so this is problem One. What is going on at my fuse box. I cleaned with fine sand paper the terminals. Added new fuses,

2, I have no dash lights with the strange exception of two lights near the Oil temp guage, I should say my guage cluster is out of the
car. No other guage lights are working. I removed my headlight switch and cleaned it and the crudy contacts, put it back in and same results. My headlights do work fine. My dimmer is mostly bright and no so bright, No real dimming. So next step is to buy a new switch to try. Question: how could i have 2 lights working when the center small 2 amp fuse was not getting voltage?

Look forward to you answers.

Fuses at fusebox have power depending upon the position of the ignition key. Only the top row of fuses are hot (BATT).
Gauge lights work, of course, with the headlight switch pulled out, and there’s a rheostat wiper that controls the voltage to the dash lamps. Not all lamps on the dash cluster are dash lamps: some are for turn signals, high beam, low fuel, etc.

Midlife, thanks for the reply. The more I play around, the more I am learning. So I still only have two lights to the Oil Guage that work with the Headlight switch on. I disconnected the clear plastic connector and tested that Blue Red stripe wire on the harness side and it had power. So does that mean that the other side that has all the lights has a bad socket or short somewhere down the line?
I had power at the very first light on the string to the Dash line but the bulb wasn’t working.
Thanks for clarifying about the other lights that are not just for gauge illumination. I get that about the ones for signal direction etc. so I will not worry about those for now. Need to determine why the other bulbs that should light up are not.
Seems like the two that go to the Oil gauge are not on the same circuit since they work with out that Connector being connected.

Midlife, I did confirm that with the key in and turned to the left for Acess. that the other fuses had power so I know my fuse box and fuses are working. I did notice with the my meter that the voltage seemed to jump around a lot before finally showing power and some showed less than others (11 volts - 12.5-7-8 volts.) I know that I seem to have power being drained from my battery if I leave it hooked up overnight. That is another issue.


There’s an OEM splice inside the dash cluster connector that sometimes fails. You should have continuity (1 ohm or less) between that pin on the dash cluster connector and all of the blue/red dash lamp pins. If not, trace the wire back and give a sharp tug on the wire going to the splice: sometimes that re-sets the connection inside the splice. Be sure to check the bad bulbs for bad bulbs (duh!).

If the OEM splice is still bad, the only re-course is to cut the wires going to/from it and start splicing them back together…a real PITA, but once done, it works well.

OK, I am new to all this wiring stuff. Is the dash cluster connector the Clear White connector in my photo? Not sure how to measure an ohm but will look into that. Do all the lamp illumination bulbs have the metal prongs? I think there are 5 correct?
So this OEM splice is in that connector or hidden under the black factory wire wrap?

Much Thanks

Yes, connect the two white molex connectors for dash cluster. Yes, all lamp illumination wires must have the metal prongs, as that provides the ground path. And yes, the OEM splice is buried under the tape.
I can’t remember off-hand whether the number of dash illumination bulbs.

Great, thanks so much for your patience here with this rookie.
So to validate one point, with the headlamp switch pulled out, all my illumination dash bulbs should all work out of the dash cluster?
If yes then i have at least 3 that dont to track down the reason which may be in the factory splice for all those wires in that lume.
I did notice if the metal prongs touch metal in the dash it shorts the fuse easily, but they should lite up even though not connected to the back for the cluster yes?
To test for ohm’s, how do I do that with my multi meter?

Much Thanks

No, you must have the bulb sockets installed in the dash cluster, as the metal housings or metal prongs are the ground points. With the bulb sockets loose, there’s no place for the little electrons to go home. The metal prongs need to touch the dash cluster and that should NOT blow a fuse. In all of this, I’m talking about the one wire bulb sockets.

To measure resistance, place the meter onto resistance: typically an upside down U or a continuous line of "W"s. One probe goes on one side of the circuit you’re trying to measure and the other probe on the other side. Continuity should be about 1 ohm or so. Set the meter to 200 ohms if you can. To see what continuity looks like on your meter, touch the two probes together.

OK, got it. I was thinking that might be the case as my cluster is not in at this time. I think I will just temporarily hook it all up to test everything. I bought a little gauge tester WCCC sells too. (You the one who makes that?)

On the second paragraph, I understand what you described and will do that and see what comes up on those tests. Just hadn’t ever done if before.
I will report back when i complete that.

Much Thanks,

I don’t make that gauge tester, but another on the forum does. I think he’s the moderator as well. I just can’t remember his forum name.

No worries. I think it might be the same person who rebuilt my fuel sender. (xr7g428?)

I pulled out my cluster wire run to inspect it better. Also wanted to get a better view of the wires and bulb sockets. I counted 6 Blue/Red wires to sockets. I bought a pack of the LED’s for my gauge cluster and it had six non-colored bulbs (meaning the body,not the lights) and six that are for specific colors on the cluster for turn signals etc. Just thought I would validate that number for you. Here are some pics. Everything looked good, had original labels on it and no noticeable damage.

Going hunting in a few days so might be week or 2 before I can tackle the resitstance testing.

Thanks again!

Well, you didn’t tell us that you had LED bulbs! Most of them are polarized, so if one doesn’t work, turn it around 180* and try again. Do NOT use LEDs for alternator indicator lamps or for the brake proportioning valve on certain years.

Those LED’s work fine for the instrument panel backlighting. The oil pressure backlight bulbs have individual grounds. The LH side of the dash requires that a screw be installed to provide a ground path.

Midlife, I didn’t have LED’s in when I started this thread, just the original bulbs. I just decided to install them now that I had the harness out. So don’t use them on the Alternator indicator lamps. That is the AMPS gauge, the first two bulbs on the run?
What is the reason? Does it effect the reading?
I have an XR7 not a Standard if that makes a difference as I know there is a different layout and guages.

Royce, thanks for your message. I figured that as they are on without the cluster installed. Assuming it is OK to use LED’s for those two? I haven’t changed those out yet.

Much Thanks,

I would not use an LED for any indication purposes, such as the brake differential pressure lamp or turn indicator lamps. Those can act funky.

An XR7 has an ammeter and not an alternator indicator lamp. You’re OK. Ammeter has only dash lamps as illumination.

Royce, are you referring to the actual turn lights? Not the guage cluster lamps. Just making sure what you are saying here on LED’s. THX

Midlife, thanks for clarifying that!
You have been a huge help.