1966 Engine/Firewall grounding issue


New Member
May 23, 2021
Hi, I am sure some of you have expereinced this issue and I hope you can shed some light on it for me. For the past five years I have been restoring a 1966 Mustand 2dr couple. I am down to the fine details now and almost ready to be finished, well as finished as one can be with a vintage car - you know what I mean.
I am having an issue getting the courtesty lights to come on. I replaced all the bulbs, door switches, checked the interior grounds and voltage checked the fuse block. All are good.
For some reason these lights will not turn on.
I turned the headlight swtich all the way to the left, nothing. Activating the door switches, nothing. Checked the bulbs and sockets - they all work. I was reading a thread that mentioned a grounding strap from the right side of the engine to the firewall. I can not locate a grounding strap. There is a "vacant" hole in the firewall, where it appears one should be mounted, but nothing there.
My question is: What other electrical components are affected by this apparently missing grounding strap? What else can I check? Does this grounding strap only affect the "internal" lighting (glovebox, underdash courtesy lights, console lights etc.?
The engine starts and runs great, radio works, headlights, turn signals, brake lights - all are working.
Thanks everyone - I will post a picture once I get everything completed.
  • Sponsors(?)


New Member
Jan 3, 2020
Adelaide, Australia
The strap between engine and car body is usually to assist the operation of the starter. It is rare for the battery negative terminal to be connected to the engine block- it usually connects to the body somewhere near the battery- hence the strap from body to block.
Are your courtesy lights and switches genuine parts or 'after-market' add ons? -- it may be they dont operate the way you think they do.

Its very difficult to give advice without actually inspecting the car/problem. As I'm on the other side of the world... that's not going to happen.... so...
Have you changed the wiring loom? ie is it standard wiring? If I down-load a '66 wiring diagram- will it be accurate for your car?

In the meantime-- someone else will no doubt offer their thoughts too....