Both door switches have been removed and test "good". Even with positive test results for the door switches I still am going to replace each door switch realizing that there may be an internal problem with either door switch that would affect test results. The wiring diagram for the '70 Mustang suggests that the circuit controlling interior lighting could be back fed by a faulty headlight switch. Any comments or suggestions about a possible fix for the problem are appreciated.
Electrical 70 Mach 1 interior courtesy lights burn with doors closed
- Thread starter 70ivygreen
- Start date
Not everyone is aware that the light switch knob has a detent and when turned CCW past the detent the courtesy lights come on. This could be your problem. Just CW from the detent the dash lighting will be the brightest, and as you continue turning CW the lights get dimmer. When using the dimmer, the light switch needs to be pulled out to either the Park or ON (headlight) position.
Below is a schematic (not a wire diagram) for a 69, which is very similar, but not exactly like a 70. The path marked in yellow shows the knob courtesy light switch:
You can see that the door switches and the light switch are all in parallel, so if any one of them is on, then the interior lights are on.
Below is a schematic (not a wire diagram) for a 69, which is very similar, but not exactly like a 70. The path marked in yellow shows the knob courtesy light switch:
You can see that the door switches and the light switch are all in parallel, so if any one of them is on, then the interior lights are on.
My '70 wiring diagram indicated that the culprit might be a faulty door jamb switch but replacing the switches did not correct the problem. The operating diagram you sent indicted that the problem had to be the light switch itself. Something internal to the switch was completing the circuit to the courtesy lights, namely the operating knob. Replaced the light switch, problem was solved. Thank you very much for your assistance.
Yes, contact D1 to D2 operates the courtesy lights via the knob. I'm glad that helped.
One of the guys on another forum says that it is getting harder and harder to get the correct style light switches and now the only thing available is a "one part fits all" universal type switch that often doesn't fit or solve the problem.
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