Author Topic: 30U Electrical Gremlin  (Read 998 times)

hursst

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30U Electrical Gremlin
« on: May 24, 2015, 10:12:00 PM »
Hello,
  I have a 30U and I'm having problems with the fuse going out all the time now.  I'm out of fuses, so thought I'd ask for some advice.  The car will start and drive just fine, but will have no lights or horn without a fuse.  If I put a fuse in and connect the battery, the fuse will heat up and break in about 8 seconds (30 Amp fuse).  I've had similar problems with the fuse going out in the recent past, both times were when I demonstrated the horn at a car show with the key off.  I would replace the fuse and be fine for a while, now, the fuse won't last at all.

  I assume I have a crossed wire somewhere or a bad ground, but wanted to ask for advice before I start taking the whole electrical system apart past the fuse point.  It's also impossible to test, as I can't get any power to the system without blowing the fuse.  I'm not very skilled with electrical, either.  Any help or advice is greatly appreciated.

frankp

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Re: 30U Electrical Gremlin
« Reply #1 on: May 25, 2015, 12:42:44 AM »
You are describing a short.  Do you smell an odor of burned insulation, see smoke from fuse block, or feel a hot wire?  It is probably worn insulation on a wire grounding itself.  Have you replaced all your wiring?  If not, look at the old stuff first especially where a wire goes through frame/fender/firewall where there will be a rubber grommet.

Since issues were with the horn initially, disconnect it and see if that corrects it.  Of course you'll need a fuse in place.  If not the horn or its wiring, examine the wiring diagram to isolate other systems such as headlights, taillight.  If you had a bad ground, there would not be enough current (amps) for this to happen, I believe.  I use a 20 amp in my '29U and the horn is independent of ignition switch.

Let us know what you find.
Good hunting,
frank
frank p

hursst

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Re: 30U Electrical Gremlin
« Reply #2 on: May 25, 2015, 01:07:08 AM »
frankp,
  Thanks for the response!  No smell, no smoke, just super hot and broken fuse.  I disconnected the horn per your suggestion and used a test light, per another suggestion from the AACA site instead of a fuse.  The light went off when horn disconnected.  Turning headlights on lit up the test light, but headlights did not come on, so it's looking like the horn.  The wiring that I can see looks fine.  It's probably 30-35 years old.  I'm suspecting the horn button and ground, as the headlights seem to be okay and they are all on the same switch wiring Clum switch at the bottom of the steering column.  Going to try the horn button/wiring now...

chetbrz

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Re: 30U Electrical Gremlin
« Reply #3 on: May 25, 2015, 01:53:24 AM »
You may have a problem with poor ground points and corroded connection points.  Each point can develop resistance and increase your total current draw.  You may have to consider checking all contact points starting with the headlights and working back to the battery.  If you find corroded connections just keep going until you repair them all.

8 seconds is a long time to wait if you have a direct short so this is why I am saying corrosion seems to make more sense, 

My 2.5 cents,  Chet...
http://www.1948Plymouth.info           Web Master - Forum Administrator - AACA member

Doug

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Re: 30U Electrical Gremlin
« Reply #4 on: May 25, 2015, 03:09:06 AM »
This will not help find the short but on my fuse holder I made an adapter so I can use the modern fuse. The glass tube ones wouldn't stay in. 

hursst

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Re: 30U Electrical Gremlin
« Reply #5 on: May 25, 2015, 02:49:16 PM »
Gentlemen,
   Thank you for all the help.  Those were all great tips and I worked off of those tips and ended up finding the problem.  It was realy 2 problems. First, I took the horn apart and the solder holding one connection to the horn lead was loose and the other end of the wire that connects to the external connector going to the main wiring harness was very loose as well.  I fixed those issues, but still no horn or lights.  I took the horn button out, checked all of that and upon re-assembly, I noticed that the horn button shaft had a lot of play in it.  I was able to tighten all that up beneath the clum switch, so now the headlight switch isn't sloppy, like it was before.  I then traced the wiring past the clum switch and what I beleive is happening is that the horn wiring within the headlight mounting bar was wearing against the horn support bolt that goes through the center of the headlight mounting bar and grounding out on it.  I didn't do a full repair yet, but I was able to get the horn and headlights working perfectly now.

  This is been an issue for about a year off and on, so nice to have it solved.  Thank you again for all the assistance!

-Chris