Intermittent exterior lights and gauge cluster problems

GR4 · Sep 18, 2024

Hi I have a 72 Mach. The headlights and tail lights, side markers, come on and off intermittently and different intervals at different times, sometimes headlights only sometimes tails and side markers only also the gauge cluster flashes intermittently and randomly all after about 10 minutes of driving time. Thoughts?

I have researched, ground wires, engine strap grounds, and bulbs themselves with no solution.

Also what does this green wire near highbeam switch go to? It’s only about 4inches long off the harness.

Thanks!!

Doug's 73 Mach1 · Sep 18, 2024

The green (light green/ red dashes) wire connects to the parking brake switch if you have the optional convenience group.

midlife · Sep 18, 2024

All of those intermittent signals appear to come from the headlight switch...check your connections there and if no help, replace the switch.

Hemikiller · Sep 19, 2024

What Midlife said...

If you've upgraded to halogen headlights, you may simply be drawing too much for the headlight circuit breaker to handle. I ended up running a relay harness for my Cibie H4 headlights and no more problems.

Retired2014 · Sep 19, 2024

+1 on the relay

mrgmhale · Sep 20, 2024

I agree with HemiKiller and MidLife (and Retired2014). I installed headlight relays on both of our 73 Mustangs, when I installed Halogen headlights. I was sure the higher current demand from the Halogen lights would overburden the headlight switch's internal circuit breaker.

https://secure.cougarpartscatalog.com/store/p/13750-Headlight-Relay-Mini-Kit-NEW-1969-1973-Mercury-Cougar-/-1969-1973-Ford-Mustang.html

The relay kit is easy to install,, works perfectly.

Omie01 · Sep 20, 2024

I also ran into this issue, the battery wire to my headlight switch was getting so hot you couldn't touch it and was causing issues. So I ordered a new switch and relay set and no problems ever since. Good luck!!

GR4 · Sep 28, 2024

GR4 said:
Hi I have a 72 Mach. The headlights and tail lights, side markers, come on and off intermittently and different intervals at different times, sometimes headlights only sometimes tails and side markers only also the gauge cluster flashes intermittently and randomly all after about 10 minutes of driving time. Thoughts?

I have researched, ground wires, engine strap grounds, and bulbs themselves with no solution.

Also what does this green wire near highbeam switch go to? It’s only about 4inches long off the harness.

Thanks!!

Update: thanks to midlife suggestion, I replaced the headlight switch and a bad side marker socket and headlights and taillights work and stay on! Thanks!

Next Im replacing the voltage regulator on the gauge cluster to see if that fixes its light problem. Also still no reverse lights but not concerned with that at the moment.

midlife · Sep 28, 2024

Voltage regulator on the gauge cluster is unrelated to dash lights: it only controls the voltage to the gauges.

GR4 · Sep 29, 2024

midlife said:
Voltage regulator on the gauge cluster is unrelated to dash lights: it only controls the voltage to the gauges.

Should I or will it make any difference if I replace the gauge cluster circuit board?

midlife · Sep 29, 2024

Unlikely, if you are still talking about exterior light issues.

GR4 · Sep 29, 2024

midlife said:
Unlikely, if you are still talking about exterior light issues.

No exterior lights seem to be fixed by changing the light switch, but the gauge cluster lights still are intermittent or not at all working at at the moment that’s why I was wondering about the circuit board on the back of the gauge cluster is that may help with those lights.

Intermittent exterior lights and gauge cluster problems

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