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Old 01/17/2017, 08:47 PM   #16
franklinair
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The fuse in question gets power FROM the Ign Switch:
Current then goes through the fuse TO the Backup light Switch, and then to the Backup lights.
Current also goes to the T/S Flasher and then to the T/S Switch (which has already been eliminated).
Other than a shorted wire, the only 2 components remaining are the Backup light Switch & the T/S Flasher.
Can you locate the connector (at the firewall, inboard of the Master Cylinder) that feeds the Backup light switch, and unplug it? That can eliminate the B/U light switch.
(I hope its not a shorted wire- that's another trouble shooting process.)

Neil
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Old 01/18/2017, 10:37 AM   #17
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Thanks Neil. That fuse also powers the radio and transmission light. Are they likely culprits?

Steve Cracknell
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Old 01/18/2017, 10:57 AM   #18
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Neil, I just looked under the hood. To the passenger side of the MC there are two connectors going through the firewall. Is the backup light connector the flat one or the squarish one?

Steve Cracknell
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Old 01/18/2017, 11:02 AM   #19
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The backup light switch is located on the side of the tranny. Neil is right on where the plug is. It is a 4 wire bugger that can be fun to disconnect. It also functions as a transmission lockout switch that only allows the car to be started in neutral or park for safety reasons. It is kinda a high wear item and susceptible to shorting out. Unplug the plug Neil suggest and that will eliminate it. My gut says not the radio or the tranny light.

Rob
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Old 01/18/2017, 11:05 AM   #20
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Quote:
Originally Posted by robert campbell View Post
The backup light switch is located on the side of the tranny. Neil is right on where the plug is. It is a 4 wire bugger that can be fun to disconnect. It also functions as a transmission lockout switch that only allows the car to be started in neutral or park for safety reasons. It is kinda a high wear item and susceptible to shorting out. Unplug the plug Neil suggest and that will eliminate it. My gut says not the radio or the tranny light.

Rob
Thanks Rob. Which of the two connectors I mentioned is the backup light one?

Steve Cracknell
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Old 01/18/2017, 01:51 PM   #21
robert campbell
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Steve,
The plug Neil describes is a 4 prong gang style plug. It will unplug both the backup lights and the neutral/park switch.

A test with a volt ohm meter could be done but direct current is funny. Sometimes a switch will work without a load (12 volt power) and will fail when the voltage is applied.

First do what Neil suggested. Unplug that plug. It is on a harness on the firewall aft of the left valve cover. Sometimes hard to see with the firewall brace being a bit in the way. But you should be able to find it. It may take a small sharp screwdriver to pry apart. Be nice to it a clean it out. Always put some lube on it before plugging back together.

So with it unplugged if your use does not pop you are getting closer. The backup lights wiring is part of the rear wiring harness. You can see the pig tails to the backup lights in the trunk wells on each side. sometimes owners love to shove all sorts of "stuff" in those trunk wells and the wire could be damaged in that area.

My guess is the backup/park/neutral switch. The test will isolate the short to this area of the wiring and switches. It is very easy to change out, but the adjustment can be fun. If it gets to that, we can step you through it.

Rob
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Old 01/18/2017, 02:43 PM   #22
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The square connector. It furnishes power to the Neutral safety switch AND the Backup lights.

Neil
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Old 01/18/2017, 03:35 PM   #23
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Thanks Neil and Rob.

Steve Cracknell
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Old 01/18/2017, 07:46 PM   #24
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Turns out the problem is in the wiring between the transmission light and the connector. I figure that with all the movement that happens when you shift from park to drive etc the wiring has possibly chafed against something. I'm going to open it up tomorrow and see what I can find

Thanks for all the advice.

Steve Cracknell
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Old 01/24/2017, 01:52 PM   #25
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Steve;
Did you locate the short in the indicator lite circuit?

Neil
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Old 01/24/2017, 02:59 PM   #26
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I haven't yet. When I first bought the car, I had to replace the bulb. After we discovered that wiring was the problem, I remembered that I wasn't too happy with the condition of that harness. I will get in there and have a look, but I am seriously considering ordering a new wiring harness and just replacing it.

Is it a difficult job to replace it? Does the wiring just go under the carpet to the trans opening?

Steve Cracknell
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Old 01/24/2017, 04:43 PM   #27
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Console? Non console? NPD sells both types of lights.
Naturally you'll have to gain access to the shifter mechanism.
The wire runs forward, under the carpet to the connector.

Neil
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Old 01/24/2017, 07:08 PM   #28
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No console. Sounds like it shouldn't be too difficult to replace then.

Steve Cracknell
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Old 01/25/2017, 06:58 PM   #29
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We found the short. The power wire (blue with red stripe) has a plastic collar inside the bulb socket which is supposed to isolate it. A tiny bit of that plastic had broken off and slid down the wire, causing a short. We were able to put some electrical tape on the wire in place of the broken bit and it's king perfectly now. I think the heat from the light bulb had made the collar brittle and it had failed.

Good to go!

Steve Cracknell
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Old 01/25/2017, 07:37 PM   #30
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Ford junk. Every 40 or 50 years you gotta fix something...

Neil
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