Jump to content
Sign in to follow this  
keithb7

Sneaky Wiring...Fun Times

Recommended Posts

I experienced a couple of weird symptoms recently in my ‘38 Plymouth. Twice I noticed the tail lights on, when the car parked and off. Hmm. I know this can be attributed to stuck-on brakes, but no that wasn’t it. Brakes were just overhauled. 
 

Then I noticed a dead battery after a few days parked. Hmm. I disconnected negative cable and charged it up. Next day reinstalled cable. Car started fine. Raining so no test drive.  I left the battery on a .75 amp trickle charger over night. Left both battery cables installed. Next morning no go-juice. The battery measures at 2V. Hmm. 
 

Time to dig in with the multi-meter and see whats going on. I ground a lead to a spark plug metal nut at the base. (great solid ground by the way). I began poking around for continuity to ground. Right off the starter lug! Ground. What the heck?   I get poking around under the dash and find grounded circuits for my fog lamps, brake lamps, running lamps.  What the heck? I must be doing something wrong. 
 

I break things down in my head  and remove any wires at the starter lug.  Hmm. Ok just the one 6-or so gauge wire is grounding. It goes up into the dash. Right to the ammeter.  The lug on the ammeter is grounding. Hmm. 
 

There are multiple wires pulled off that one ammeter lug. So each one of those circuits are now being grounded. I remove all connections at ammeter and start checking each one. Now I’m down to only 1 wire that is grounding. Hmm. Where does it go? I’m thinking about the brake lights coming on a few weeks ago. Likely to the brake lights I figure. Sure enough. Indeed it does go to the brake lights. I check continuity at the brake switch, affirmative. Remove wire after switch that goes to the brake lamps. Continuity test wire from ammeter to brake switch connection, all good. No grounding.  Remove wire at brake switch that goes to brake lights. Bingo! Its grounding.  


This is fun. Making progress. Yet now its time to get under the car. Maybe even drop the fuel tank to see what I’ve done. I built the rear harness from scratch. I screwed something up.  Time to don the coveralls and get under there. 
 

I’ll report back my findings. I think I'm getting close.
 

I am grateful how simple these old cars are. I was amused and reminded how tricky electrons and wiring can be. 1 simple wire was pulling down everything else that it touched. Where it gathered at the shared lug on the rear of the ammeter. A few years ago I would have been on a wild goose chase after I found several different circuits grounding. Sometimes aging is not so bad. I've learned to slow down and think. Lol.
 


 

 

30722A36-E250-4222-A7BD-C0B0DF058DB3.jpeg

Edited by keithb7

Share this post


Link to post
Share on other sites

Note to future self: Single wire in-series light circuits, all circuits after the switch go to ground. Its when they don’t go to ground is when there’s a problem! 
If said circuits go to ground before the switch, there’s a problem!  
 

Turned out to be a failing brake light switch. All my harness wiring seems to be fine. Hydraulic actuated brake switch was making contact at switch when the brakes were released.  Brakes lights are wired directly to the battery circuit. Battery was draining.  Replaced switch all seems good.  I think!  I may be back to ask for help...

 

 

ACCC4920-5677-404A-A21D-8FC6ABF654B4.jpeg

Edited by keithb7

Share this post


Link to post
Share on other sites

Are you sure your brakes are releasing fully?  Have you checked the relief hold in the bottom of the mc reservoir to make sure it's open.  Do you have suffient Freeplay at the top of your pedal stroke?  These can lead to not releasing the switch and keeping tabs lights lit which of on for long enough can now the fuse or trip the breaker.

Share this post


Link to post
Share on other sites

The old switch was done. Even when removed it was making continuity. Thanks for the tips though. I will be sure to double check everything else. Brakes do release properly. All new hoses. MC rebuilt. Jacked, up the wheels turn nicely.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
Sign in to follow this  

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.

Terms of Use