‘34 lights/electrical mystery

[Digger]

On my 34 coupe that I’ve had for years, the juice brakes were kind of tight, and the brake lights were staying on. The headlights and cowl lights worked perfectly fine. This is a 6 V stock system. Brake light wire connections on the end of the master cylinder.

I have been using an optima battery, and had it for a long time, so I replaced it. I also replaced the starter because it was turning relatively slowly. Upon putting both of those new items in, it did help the starting of the car, and the brake adjustment was perfect. But now mysteriously, none of the lights work. I checked the bulbs out of the car, and it is not the bulbs. I swapped out the fuse for several new ones, that did not help either. Horn works and stock amp meter works.

Any thoughts as to what it might be? I did not touch any electrical wiring, screws, nuts, bolts, anything at all, just changed the battery and the starter. Any comments appreciate it. Thank you, Barners.

[drolston]

I presume you checked the fuses that came out were not blown? Check with an Ohm Meter?

[cas3]

You don't have any slack in the master cylinder push rod, so the piston can't return its full stroke which will block the port that lets the pressure off., and brake lights off. Need just a wisker of play on the rod going in to the master

[deuce_roadster]

Not the problem but it looks like I see 12v (too small) wire gauge in there too.

[koates]

You say you have a stock 6 volt system but a stock system has mechanical brakes not hydraulic. As already stated make sure the master cylinder push rod has a little free play so as not to hold pressure in the line which would keep the stop lights ON. I note that the under dash fuse is not seated in the fuse holder correctly, its off to the left side a bit. Correct that and make sure the fuse holder ëars"are good and tight on the fuse ends. Get hold of a test light (a 12 volt screwdriver one will work) and test both sides of that fuse for power. If it has power then remove and open up the headlight switch on the bottom of the steering box and see if you have power down there. You need to do testing with a test light or a voltmeter to find where the power is lost. Just guessing is not the way to do it. Read a wiring diagram to see how circuits are connected. The drivers handbook has a diagram. Regards, Kevin.

[Digger]

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Thank you for the advice, will follow up

[slowforty]

Use a meter to check voltage. Test light only tests voltage. Not the amount. Went nuts testing a circuit had light, but not enough voltage to operate the brake light.

[koates]

Originally Posted by slowforty

Use a meter to check voltage. Test light only tests voltage. Not the amount. Went nuts testing a circuit had light, but not enough voltage to operate the brake light.

Thats a strange statement. In my 60 years in the auto electrical trade I have found it often quicker to use a test light to test for good power in a circuit. A test light uses current where a meter uses very little which might be a problem in a circuit with poor connections to supply good current. Of course if you actually need a voltage reading then a voltmeter is necessary. On modern cars with electronics a test light might cause problems or damage and therefore a digital voltmeter or a low current draw LED test light would be safer.