Fun with Backup Lights

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Fun with Backup Lights

Postby Landon » Sat Apr 07, 2012 2:15 am

Thought I'd share this latest experience, getting my backup lights to work.

79 J10
258, D20, T18

Why didn't the backup lights work?
When we inherit these trucks from previous owners, it's like unearthing history to fix things anywhere close to factory, or the way it should be. Working back to front....

1. No bulbs in sockets (stole from the 124 Mercedes)
2. Overspray (primer?) prevented a ground between the socket and the taillight housing, both sides.
3. Exposed bare wire between driver's side and passenger side housings. Replaced with butt connector.
4. Backup switch wires not hooked up.
5. Backup switch trashed, had to replace
6. Replacement switch does not match connector, build jumpers
7. No 12V at switch, traced the wire through the bulkhead connector, back out into the engine bay, and to the open connector with nothing attached.

This is when it got interesting. The White/TR 18 ga wire runs in the loom along the firewall to a flat female connector, that would receive a 4 pin small blade connector. I don't see one on the truck.
I hooked 12V to the wire at the connector, and Hey, reverse lights!

What is that connector for? I measured for voltage and found orange and red wires are hot in run. Hmm. can I use one of these circuits with a jumper for the reverse light feed? Why not?
I first jumped the orange to the white/tr and turned the key and shifted to reverse, and a faint light from under the dash came on....hmm, oh, courtesy lights? No, it goes in that socket there, what is that? Looked at the dash...

"4 WHEEL DRIVE"

Ha!! I laughed and told my wife I had it fixed, to come try it. She was only mildly amused. "I think you have your wiring crossed." Uh-huh.
So then i jumped it from the red to the white/tr, shifted to reverse, and voila, 8 hours and a new reverse switch later, we have reverse, ahem, backup lights!

And I have a plan for the 4 Wheel Drive indicator. I believe it's circuit was looking for a ground and found it backwards through the reverse light bulbs.

Red supports several loads, the carb solenoid, electric choke,
the White/Tr leads to the backup switch and then the lights and they ground to frame.
Orange would go to the Four Wheel Drive switch that would close when engaged and return to the black and the black is ground to complete that circuit, allowing current to flow through the bulb in the dash, that makes sense but I didn't get continuity between the black terminal and ground.....now about the 'Low range' indicator....hmm. No idea.

8. Built a jumper and used one of the circuits to power the backup lights. (after detour into 4 WHEEL DRIVE Indicator)

Reminds me of Apocolypse Now: "Where's your CO ?" (read Neutral Safety Switch) "There's no Neutral Safety Switch here"

Target is beach fishing Padre Island May 18th. Gotta get registered.

- Landon
Landon
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Location: Austin, TX

Re: Fun with Backup Lights

Postby Elliott » Fri Jun 15, 2012 9:38 am

Bwa ha ha.... I hate wiring.... :funnypost:
Elliott
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