'73 Coupe DeVille electrical problems (Please Help)

[thevinylking69]

The other day I flipped the power lock switch on the drivers door and I heard a sizzle and smelled burning plastic, now the power locks power seats, running lights, horn, blinkers, flashers, interior lights and climate control system do not work anymore. But NO fuses are blown. Today I removed the front seat and the blinkers ONLY started working again, everything else is non functional. I disconnected the battery to prevent fires and further damage, but I would really appreciate some help or guidance to where the problem may lie. Any help would be greatly appreciated, because I dont feel safe driving the car with these problems, and I'd really like to get my daily driver going again.

Extra info: I'm 19 and very handy, this is also my first classic Caddy, but I've always loved classic Cadillacs

Thanks for any info you provide,
      Chuck

[Dave Shepherd]

No short cut here, start looking for a burnt harness in the circuits involved with those accessories, start at the fuse panel, There is no common fuse or circiut breaker for those components, check the fusible links at the starter harness also, but something caused this so pinpointing the problem is number one.

[mgbeda]

Sounds to me like one of the fusible links from the starter.  Particularly the one that does NOT go through the ignition switch; i.e. the circuit is on all the time.

Assuming the fusible link is burned out,  as Dave says some short or overload must have caused it to burn out, and that is presumably in the power locks somewhere, or in the driver's door (a short that happened because of moving the switch or the lock linkage).

You are smart to not drive the car until you find the problem- you don't want an electrical fire breaking out.

-mB

[thevinylking69]

What would a fusable link look like or be located? Would downloading the shop manual help me out with this problem?  Also, thank you both for your replies, i'll keep you updated on my progress

[Aaron Hudacky]

Chuck,

A factory shop manual will be helpful because you can trace any circuit related to the power locks, as well as fusible links, etc. When I was 19 the power seat caught fire in my 72 Sedan deVille, so I sympathize with you.

It may go without saying after your experience, but having a fire extinguisher and tools to disconnect the battery in the car are invaluable.

[TJ Hopland]

You are going to have to figure out what happened to cause the link to blow.   My first guess would be the harness between the door and body.   Lots of flexing there over the years.

The fusible link wires are all attached to a single lug that is on the big stud of the starter along with the big wire from the battery.  There are 3 link wires and a total of 5 wires in that harness.   One wire is the signal from the key to crank the starter.  Another wire goes to the ignition coil to give a 'boost' during starting.  The link wires are about 18" long then transition to regular wire.  Just after they turn to regular wires they and the other 2 go into a connector.  This connector gets full of crap from the road and leaking off the engine.  It also often gets tangled up with the exhaust and is melted or damaged from the heat.   One of the link wires feeds the headlight switch.  One feeds the key and then the half of the fuse box that comes on with the key.  The last one feeds the half of the fuse box that is always on.   The link wire is available at parts stores and its color coded by gauge.  The combination of gauge and length makes up the rating.  Sometimes the problem with them is the transition to the regular wire, it corrodes and looses the connection.

It looks like an #18 green link wire to #14 yellow regular is the one to the headlights.  The other link wires are #16 black.  One turns to a #10 red / black stripe and is the one that feeds the always on fuse box.  The other one turns to a #10 red and is the one to the key switch.    The only connector they are showing is the main bulkhead connector on the firewall.

[mgbeda]

What TJ said.

I do agree you need to find out why the fusable link blew (if that's what blew) but I don't think you'll be able to find that out without getting power back into the circuit, at least temporally (you'll want to be able to disconnect the power in a big hurry if you get the sparks again).  Fusable links can go bad from age (oil and heat degrading the insulation like TJ said) and if they aren't routed just right they can touch the exhaust, melt and short.  But you had an Event when all this first went bad so it seems the fusable link is a symptom, not the problem.  What's weird is that the Event didn't blow a fuse, which are supposed to go out before the fusable link.  The power locks, if I recall, have a circuit breaker instead of a fuse.  Could that have gotten stuck over the years so it wouldn't trip?

A wiring diagram would be a big help to you.  The Cadillac chassis shop manual does have detailed ones, or I think you can get them separately.

I think what I would do is to 1) turn everything off 2) Check for voltage at the fuse box for the always on circuits (like seats, hazards, interior lights, etc.)  If they are all dead at the fuse box, that sure would point to the fusable link.  Check both sides of the fuse for current, just in case a fuse blew but you missed it.  3) if those circuits are dead then, at the fuse box, place a jumper between a circuit that's only on with key and one of the dead circuits.  You'll want to be able to pull this off in a hurry if you get sparks again (before you blow another link) so don't attach it very tightly.  I'd have it so I had to hold it in place myself. 4) turn the ignition on (without starting the car).  Now you should have power to those dead circuits again (by bypassing that link).  See what works, always being ready to cut the power quickly.  5) If you can repeat the problem by using the power locks, then you can pull the power lock circuit breaker and then fix the fusable link.  Then you can drive the car until you can fix the problem properly.

Good luck.

-mB

[Glen]

One of the tricks I learned is to use a light bulb in places like this.  Wire it up in place of the fuse/fuseable link.  If you have a dead short the worse thing that can happen is the light glows bright.  As you troubleshoot the problem keep an eye on the light bulb.  Pull fuses in the circuit.  When you pull the right fuse the light will go off.  Put the fuse back in then go down the line and disconnect things.  Again when you disconnect the problem the light will go off. 

[TJ Hopland]

The light bulb is a good and safe trick.