Power Antenna Switch Meltdown

[Gary S.]

Can anyone suggest what happened in this situation? I put carpet in a 66 this week for a friend. After getting it done, I drove it down the driveway....then smoke and the stink of burning wires came from the dash. I thought she was going up in flames. Inspection revealed the pigtail hot wire on the power antenna switch melted...clear up thru the plug and back thru the main harness to the common connector for that hot wire which is behind the left side of the gauges. This car has a fixed antenna on it now, but inspection shows it to have the plug on the antenna end plugged into something....maybe a left over motor. It has the muffler on so hard to see. The main wire harness is relatively new. I removed the steering column and gauge cluster, cut open the main wire harness, replaced the wire from the common connection to the plug the power antenna switch plugs into. I can't see anything that would have caused this. It surely makes one's heart weak though. Gary

[Wayne M.]

Re: Power Antenna Switch Meltdown

..... The main wire harness is relatively new. ...., cut open the main wire harness, replaced the wire from the common connection to the plug the power antenna switch plugs into. I can't see anything that would have caused this.

Gary --- Let me take a stab at this [just a hunch]. I assume you were not operating the P/Ant. switch when the short circuit was underway. Sounds like the problem is in the switch (was it recently rebuilt / repaired ?) and that the red 14 gauge 12v switch feed was somehow simultaneously in contact with BOTH the up (14 ga. black w/white stripe) and the down (14 ga. blk) wires. This would explain why the red feed was cooked, yet the up/down switch outlet wires were not. [the switch itself is mounted on fiberglass -- no ground source there]. The ultimate ground routing would be to the rear harness and thru the motor (both up and down are indirectly "grounded" to the frame, but through the motor armature, which translates into rotation. Maybe the motor is frozen. If the problem was NOT in the switch, but only due to shorts in the antenna motor, then the overheating would only happen when the switch was held in up or down direction.

The reason I say both up/down switch outlet wires, is because if it was only one, it would also show signs of heat damage (how do the up/down wires look at the multi-connector to the rear harness clipped to the birdcage support behind the left side of the instr. panel ?). The high current from switch inlet red 14 ga. was then split into two outlet 14 ga. wires, which were sufficient to carry this current without damage.

Same thing on the upstream side. Examine the 12 ga. (main feed from engine harness to inside) red wire at the firewall multi-plug; any evidence of heat damage ? You say you replaced the P/Ant. 14 ga. red wire in the main (under-dash) harness back to the junction (soldered within the harness) where the main feed splits to various 12 and 14 ga. branches. Again, if my thinking is logical, the damage may have not occured in the main feed 12 ga. red because it can carry the current (without damage) that would cook a single 14 ga. wire. Essentially, the limiting resistance was the single 14 ga. red wire; all others in the circuit could carry this excess "shorting" current.

Just a thought .

[Edward J.]

Re: Power Antenna Switch Meltdown

Gary When That Red Wire Melted Something Had To Of Grounded It To Metal, That Wire Would Be Hot With The Key On (meaning 12volts All The Time) And That It Wasnt Fused At The Spot The Wire Grounded -did You Remove Fuse Block For Carpet Install ,or Possiable Screw Pierced The Wire Somewhere Near The Fuse Block.

[Wayne M.]

Re: Power Antenna Switch Meltdown

.... That Wire Would Be Hot With The Key On (meaning 12volts All The Time) And That It Wasnt Fused At The Spot The Wire Grounded.

Minor point -- the '65-6 power antenna doesn't need the key to operate, and the circuit is unfused [except for a circuit breaker in the P/A motor (I believe)].

So the short would begin the moment the battery cables were connected, or when the P/A switch pigtail was plugged into the main harness, if the short was in the switch.

[Edward J.]

Re: Power Antenna Switch Meltdown

Wayne All Circuits Should Be Fuses By Some Means To Protect Against Short Circuts ,so When Theres A Meltdown Its Before The Fused Area,a Circut Breaker Will Contiune To To Go On And Off Until Failure Of The Breaker , Then A Melt Down. Im Not Looking At A Diagram, Ive Been A Mechanic For 30+ Yrs.

[Gary S.]

Re: Power Antenna Switch Meltdown

Thanks to all of you who have replied, it is much appreciated.

I should have added more to my explanation, but it was long enough as is. I did look at the wiring diagram before repairing and the power antenna switch is hot all the time, no ignition key needed. It is not fused, but it is connected in the circuit breaker along with the cluster of hot wires. I unplugged this switch at the beginning of the job as well as disconnecting the negative battery cable. When I finished the carpet job, I hooked everything back up and tested all....radio, blower, etc. All was fine. I also flipped the power antenna switch up and then down, heard no motor noise and then realized it had a fixed antenna on it (this may have been the beginning of trouble). I thought I might have pinched the wire with a radio side panel screw too...but no. I think either this PA switch malfunctioned or the other end of the plug is connected to a non-functioning left-over power antenna motor still mounted on the bracket that has a problem. That rear end of the PA wire is plugged into something back there where the motor is, but can't see too much as the muffler is in the way. The owner came and drove away yesterday and no issues.

Probably not worth anyone else's time. I just thought maybe someone had experienced a PA switch meltdown.