I have a '68 roadster and a question about the door switch that operates the interior lights. When I push the switch in, the lights dim but do not go out. I wonder is there is a problem with the switch, or possibly a short.

Thank you for your help.

 

Does this happen with both doors? If so, I'm not sure how to troubleshoot that one, but if just one read on.

Yes it's shorting to ground -- but that's how it's supposed to operate! The body of the switch is connected to the chassis ground just by being screwed into the hole. The plunger has a metal disk at the far end which is "hot" from the harness wire. When the plunger is extended, the disk makes contact with the body of the switch, completing the circuit – when pushed in, the disk is supposed to separate from the ground path and disable the circuit. It sounds like your plunger and disk connection is wonky... or your wire is making contact with the post framing somehow.

Unscrew the switch from the hinge post and gently pull the switch and wire out a few inches. Be careful because the wire is connected to the switch with a tiny spring connector. (Replacements are readily available but no need to R&R if not needed.) Does the wire show any fraying which could be making contact separate from the switch? Examine the metal disk on the plunger just ahead of the wire connector - it should be insulated from the plunger with its plastic mounting. Grease the plunger and internal spring so it operates smoothly and work the plunger in and out. Check the insulation on the wire to ensure it is intact as far from the switch as you can reach - you can remove the side kick panel for more access to the wire. Try this and post a pic or two of what you've got.

There's a separate issue where the plunger's extension may not be enough -- does this plunger's extension from the mounting nut match the extension on the other door? They are self-adjusting but I'll leave that for a follow-up reply.

 

That switch does not "pass power" to the lamps; it passes electrical ground to them. So, pushing the switch does not COMPLETELY break the ground connection. Does it do this only when you are closing the door? Or does it still act the same when you manually push it?
If only when closing the door, you are probably missing the little rubber cushion that was placed on the door where the plunger was to make contact with it. If it happens all the time, there is some built up corrosion in the switch that allows some amount of electrical transfer thru the switch (when it should not).

 

When the lights dim its finding its ground through a separate path. You have a short and it may be at the light switch or in the associated wiring. The switches at the door could be folded over and you are getting a week ground that isnt enough to give you full voltage. Those switches if operating correctly wont dim with a little bit of connection...it needs resistance to lower the voltage to alter the output of the lamp. They do make a tool that would help you trace the ground but I havent had to purchase it and test it yet. The tool is a self powered probe that tests grounds, provides power to test circuits and can also to for shorts. If you have the time I would check for issues with the white wires. Atleast my 68 the wires are white. They run under the carpets, behind the seats to both doors and up the sills. You may need a wiring diagram to find them all and trace them correctly. YOu could also disconnect the rear harness to see if ht eisssue goes away. If it does then its in the rear harness and lights, if it doesnt you know its either the switches or the front wiring

the tool is like this one

 

Yes, dimming only happens on driver's door switch.

Here are pics. Very little wire available to pull through. I don't see any spot on wiring for a short. I sprayed with contact cleaner but no help.

Thanks for your suggestions.

 

Switch is likely defective inside it. There are two little contacts which are shorted by a washer when the spring loaded plunger is released. If the washer is stuck to the contacts (corrosion, etc), the connection will remain.

 

What is the black wire spliced into the white wire....thats not stock...where does it go?

 

Good question. Looks like someone tapped into that [sometimes] ground line for some reason. Did a PO try to rig up a 'dimmer' into the '68s interior light circuit?

 

Perhaps the PO tied into the line for an aftermarket alarm??? Jerry

 

Either way, it could provide some "ghost" ground path for the interior lights. Those splice clips are easy to 'open', then use needle nose pliers to pull out the shorting bar. That way you disconnect the 'mystery' wire without cutting any wires. And you could put it back together....if you ever find what its reason for being there AND you decide to keep it.
Pull it apart and see if the interior light 'problem' disappears.

 

Thats what I was thinking...white is power not ground in that circuit...

 

The white wire is just a "transfer" line between the two interior bulbs, which connect to electrical ground when the jamb switch is made. There is a "hidden" orange wire between the two bulbs for the power line.

 

Yes the main power does com in on the orange, but with the door switch disengaged it will show power on the white wire....until the switch is closed connecting the ground, completing the circuit.....IF that spliced black wire has any type of resistor/ rheostat on it you will get a dim bulb when the switch opens removing a clean ground

 

Hmmmm.. Yep, voltage will flow thru the filaments of the bulbs into that white line, when the ground(s) are disconnected...no current flow, of course. Unless, there is something drawing from the black wire (and allowing the lamps to glow).
Good observaction. DING, DING, DING We have a winnah......

 

Thanks for the interesting conversation. I bought this car in 1983 from the original owner (who was an engineer at Motorola), and he put an aftermarket alarm in it! Still works. I will take that splitter apart and see if that solves the problem. Ken

 

Aha!! Disconnected "extra" wire and all door switches now work fine. Here's the culprit! Thank you for your brainstorming and solution. If any of you get up to Door County, WI, please stop by. I always have beer in the garage frig

Thanks again. Ken

 

That alarm should have some kind of key switch or other 'activation' method. Do you know "where" that might be? If the alarm system was turned OFF via some method, it would not have put any kind of drain on that white transfer wire, I believe. Either way, that jumper wire should have gone to a relay in order to power the alarm. Perhaps the alarm system doesn't work [for whatever reason] but it was actually in the ON position. If you learn more about the alarm system and how it is connected in to the electrical system (ie, what does that black 'spliced-in' wire feed? How is the alarm system engaged?), you may be able to salvage the benefits of that alarm system without disconnecting it OR by re-routing the feeder wires for it.

 

So is that black gadget the alarm?👆

 

That is the siren portion of the alarm mounted on the passenger side inner fender.