Only the DASH Illumination Lights don't work

Help Support 7173Mustangs.com:

Parkka

Well-known member
Joined
Jan 12, 2019
Messages
129
Reaction score
13
Location
New England
My Car
73 Mustang Convertible
[url=https://ibb.co/cgCFb3N][img]https://i.ibb.co/j6WMVfL/IMG-20190713-145003409.jpg[/img][/url]
I tried to trouble shoot this for over an hour and I believe I have isolated where the electrical problem may be coming from.  After getting all of the instrument lights to work and reinstalling the cluster back into the dash, only the illumination lights of the dash went out.  I also heard a faint snap; similar to a short in the lower left corner of the instrument cluster or headlight switch.

Things that still light up:

dummy warning lamps

gas gauge works

flashers lamps

turn signal lamps

high beam warning lamp

and each of the illumination bulbs also worked after taking them out of the cluster and testing them on a 9 volt battery.

The headlights, emergency flashers and the turn signal lights OUTSIDE of the vehicle also work.

I already replaced the circuit board and the voltage regulator prior to this problem and every thing worked earlier before I tried to flip over one LED light to get in on. With various warning lamps and gauges working (beyond the illumination of the dash) I don't think the circuit board or the voltage regulator shorted out, but I may be wrong.

So, my question is whether or not the 'headlight switch' may have a problem with a wire burning out.  Is there a single wire which illuminates the dash?  When the headlight switch is pulled out to either the parking lamp position or the headlights, the dash lights do not come on.

Like I said, I tried to isolate this to make it easier for anyone that can help.

Thanks again,

Dan

 
Joined
Jan 1, 2012
Messages
8,177
Reaction score
932
Location
Springfield, OR
My Car
1971 Mustang Sportroof M code
Yes, either the headlight switch or the fuse. The snap you heard may have been the fuse.

There is one wire that runs from the headlight switch to the fuse panel, then it branches out after the fuse.

 

midlife

Shorts checker
Joined
Jan 24, 2012
Messages
4,111
Reaction score
526
Location
Tucson, AZ
My Car
No Mustangs at the moment.
Dash lamps are on a completely different circuit than turn signals, high beam, and gauges. Yes, your description indicates a problem with the headlight switch (where power for the dash lamps originate), the rheostat on the headlight switch, the smallest fuse in the fuse box, and the wiring between the headlight switch and the fuse box, and from the fuse box to the dash cluster connector pin.

 

Parkka

Well-known member
Joined
Jan 12, 2019
Messages
129
Reaction score
13
Location
New England
My Car
73 Mustang Convertible
[url=https://ibb.co/cgCFb3N][img]https://i.ibb.co/j6WMVfL/IMG-20190713-145003409.jpg[/img][/url]
Thank you.

Now that we have narrowed it down to the headlight switch, is there a possibility that the problem is actually with the connector plug off the wiring harness to which the switch snaps into? If so, does anyone know which wire off the plug would run the dash lights and which wire I would jump too in order to get a currant to see if the lights turn back on to finally isolate the problem? It is easier to replace the switch and I'm hoping this is the fix, but if not, it is going to be a real pain to repair and diagnose the plug without the proper wire(s) identification.

Also, just put the car in a dark garage and found the light for the automatic shifter lights up, so that is good.

I hate these small bugs that arise after rebuilding the whole car from the bottom up.

Dan

 
Joined
Jan 1, 2012
Messages
8,177
Reaction score
932
Location
Springfield, OR
My Car
1971 Mustang Sportroof M code
The wire is light blue with a red stripe.

Did you check both sides of the fuse to see if it has voltage to it, with the switch turned to full bright (clockwise)?

 
Last edited by a moderator:

Parkka

Well-known member
Joined
Jan 12, 2019
Messages
129
Reaction score
13
Location
New England
My Car
73 Mustang Convertible
[url=https://ibb.co/cgCFb3N][img]https://i.ibb.co/j6WMVfL/IMG-20190713-145003409.jpg[/img][/url]
ok. with the headlight switch pulled out one detent to the parking light position and the rheostat turned to full bright, the continuity setting on the voltage meter sings like a bird.  all fuses and fuse connections and the fuse itself are good in the fuse block.  The climate control also does not light up; as they are connected to the same wire set for the dash illumination.  Does this now sound like the headlight switch is bad, or is it the wire in the plug or as it leads out to the main harness?

The phots attach illustrate the fuse box and the back of the headlight switch still attached to the back of the dash.  I can now see the blue wire with the red stripe Don and I thank you for that clarification.

Dan





 
Joined
Jan 25, 2017
Messages
715
Reaction score
16
Location
Tavares, fl
My Car
71 Mustang Mach 1
302-2v
C4

I had the same problem with the illumination lighting. I also had Several of my marker lights and tail lights were really bad rusted and corroded and were intermittently working. After replacing those and the headlight switch everything works great now. I was able to find a 1971 OEM headlight switch on ebay for a good price.

 
Last edited by a moderator:
Joined
Jan 1, 2012
Messages
8,177
Reaction score
932
Location
Springfield, OR
My Car
1971 Mustang Sportroof M code
Most likely the headlight switch or the connector to the headlight switch. Did you measure the voltage at the fuse? No voltage at the fuse with the switch on and turned to full bright will confirm that the problem is prior to the fuse (headlight switch), and not in the wiring after the fuse.

 

rocketmans2k

Member
Joined
Jun 15, 2019
Messages
23
Reaction score
0
Location
Houston, TX
My Car
1973 Mach I Q Code w/toploader
I have a similar problem. No voltage at either side of the fuse with rheostat full clockwise and switch pulled out to the first detent. All marker lights and tail lights working. Is this almost surely the switch if the fuse is good? Interior lights light up when rheostat is full CCW.

 
Joined
Jan 1, 2012
Messages
8,177
Reaction score
932
Location
Springfield, OR
My Car
1971 Mustang Sportroof M code
Most likely either winding in the rheostat is broken or the brush (carbon rubbing block) Is missing or worn out. The other possibility is the wire connection at the headlight switch or fuse block is bad, also possible that the wire has been damaged.

 
Last edited by a moderator:

rocketmans2k

Member
Joined
Jun 15, 2019
Messages
23
Reaction score
0
Location
Houston, TX
My Car
1973 Mach I Q Code w/toploader
Thanks Don. I thought getting the car running was going to be the hard part. Now it's getting everything working properly so I can pass inspection.

 

Parkka

Well-known member
Joined
Jan 12, 2019
Messages
129
Reaction score
13
Location
New England
My Car
73 Mustang Convertible
[url=https://ibb.co/cgCFb3N][img]https://i.ibb.co/j6WMVfL/IMG-20190713-145003409.jpg[/img][/url]
The problem remains here...replaced the switch with an original Ford product still in its box...$$$$

Still no dash lights, but all of the warning lamps and gas gauge remain working.

I also noticed the climate controls do not light up; as they are married with the instrument lights.

I'll need to chase the wiring to see where I finally get a current and then move forward again from there. however that is now placed on hold as I just found another problem that has reared its ugly head; it appears my brake booster is making a sound under the dash similar to a woopy cushion when the brake pedal is compressed. The brakes then become extremely hard to compress. After a few pumps, the power assist returns and it feels normal. Not sure if the diaphragm is unseated or ripped.

Dan

 

rocketmans2k

Member
Joined
Jun 15, 2019
Messages
23
Reaction score
0
Location
Houston, TX
My Car
1973 Mach I Q Code w/toploader
...and a Whoopee Cushion sounds like a fart, so that's an amusing problem you've got there. I wonder if Monty Python ever did a skit about a farting car?   :D

 

Machvince

Well-known member
Joined
Jul 15, 2018
Messages
94
Reaction score
13
Location
France
My Car
73 Mach One Q code
Euhh Got the same problem : no more light on the dashboard, but all the others are ok..

I read "rheostat" , is it to adjust the power of the light ? and where is it ? didn't found it yet. :(

(73 mach 1).

 
Top