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06-22-2009, 09:16 PM
|  | Enthusiast | | Join Date: Sep 1999 Location: Boilermaker Country USA
Posts: 286
| |  Reverse Backup Switch Resistance Help
Ok, now with the fuel sending work we are onto the reverse switch mounted on top of my T-176 tranny case. A lot of the times the reverse lights stay on all the time. Sometimes the lights are off when moving forward. I unscrewed the switch with a 15/16 socket. Bench tested it and got a closed circuit of 7 ohms. Screwed the switch back in, hooked up the DVM, and got in the range of 85-90 ohms (with the tranny in reverse, out of gear we infinite overload). Is this reasonable, right, wrong, or a switch bad? The red and white pig tail was not connected when we check this resistance. What do you think?
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1985 CJ with a transplanted 94YJ 4.0L motor, T176 tranny, mainly stock otherwise. ><>
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06-22-2009, 09:27 PM
|  | Moderator | | Join Date: Dec 2001 Location: Belleville, Illinois
Posts: 9,602
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Are you testing between the pin on the switch and the transmission case? Seven ohms is high for a switch like that. You should get less than 1. Actually it should be almost indistinguishable from the resistance of the meter leads. With it screwed into the case you should get essentially the same reading, within a few hundredths. The 85 to 90 ohms is enough to keep it from working. Did you use a thread locker or lubricant on the threads? I wouldn't expect that to cause any significant resistance, but don't know what else it could be.
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06-22-2009, 09:40 PM
| | Enthusiast | | Join Date: Sep 1999 Location: Boilermaker Country USA
Posts: 286
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Quote:
Originally Posted by Jim_Lou  Are you testing between the pin on the switch and the transmission case? Seven ohms is high for a switch like that. You should get less than 1. Actually it should be almost indistinguishable from the resistance of the meter leads. With it screwed into the case you should get essentially the same reading, within a few hundredths. The 85 to 90 ohms is enough to keep it from working. Did you use a thread locker or lubricant on the threads? I wouldn't expect that to cause any significant resistance, but don't know what else it could be. | No, we are testing between the two pins on the switch. We did not use thread locker or any lubricant. When the switch is installed in the tranny, are you to test between one pin at a time with one lead to the tranny case itself? Is the reverse switch to have one or two pins? Thanks
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1985 CJ with a transplanted 94YJ 4.0L motor, T176 tranny, mainly stock otherwise. ><>
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06-22-2009, 10:05 PM
| | Moderator | | Join Date: Dec 2001 Location: Belleville, Illinois
Posts: 9,602
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Some have a single pin and ground the circuit when in reverse. Others have two pins and pass current through. If yours has two pins and two wires to go to them then that's the way it's supposed to be.
I don't understand how you're getting a different between the pins when it's in the transmission, but am fairly sure that the switch is bad. The remote possibility is that th einternal linkage isn't fully engaging the switch when it should, but it's pretty unusual for a switch like that to have a half-engaged position. Replace the switch - it's not expensive.
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EVERYTHING's easy for the guy who doesn't have to do it. B. Dash Fabrication |
06-23-2009, 03:32 PM
|  | Addict | | Join Date: Mar 2009 Location: So.West Indiana
Posts: 423
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Jim is correct, you should be showing about 1 Ohm or less when the trans is in reverse.
And you should be showing 'OVER LIMIT' resistance when the trans IS NOT in reverse...
Sounds like the switch has given up internally.
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One thing I want to point out,
I don't think Jeep ever used it,
But some vehicles use a NEUTRAL SAFETY switch and Reverse light switch in the same housing.
You might try checking the pins to ground, one in neutral,
The other to ground in reverse.
Either way you shouldn't be showing 70 to 90 Ohms BETWEEN them...
Open (Over Limit) or under one Ohm should be the readings...
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So Many Cats, So Few Recipes...
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06-23-2009, 05:18 PM
| | Way Outta Control | | Join Date: Sep 1999 Location: usa
Posts: 10,698
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It's a switch, not a resistance! ANY resistance is unacceptable.
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Too many idiots on the SWB to bother with them.
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06-23-2009, 09:12 PM
| | Enthusiast | | Join Date: Sep 1999 Location: Boilermaker Country USA
Posts: 286
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Thank you guys. I appreciate you taking the time to share some of your wisdom. I have ordered a new backup Light Switch for my T176 tranny, part #52449.0252 from Quadratec at $12.99. I will check resistance values of the new switch, compare to the old, and report back. Thanks 
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1985 CJ with a transplanted 94YJ 4.0L motor, T176 tranny, mainly stock otherwise. ><>
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06-24-2009, 12:09 AM
| | Addict | | Join Date: Mar 2009 Location: So.West Indiana
Posts: 423
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Quote:
Originally Posted by RRich It's a switch, not a resistance! ANY resistance is unacceptable. | Every conductor shows some resistance... Unless it's a super cooled super conductor.
Just like every switch will show some 'Bleed' when it's open.
Lubrication and ionized moisture will show some conductivity even when the switch contacts are open...
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So Many Cats, So Few Recipes...
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06-24-2009, 01:23 PM
|  | Official Curmudgeon | | Join Date: Nov 2001 Location: Kansas
Posts: 4,333
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Quote:
Originally Posted by RRich It's a switch, not a resistance! ANY resistance is unacceptable. | Then you can’t have one. Quote:
Originally Posted by TeamRush Every conductor shows some resistance... Unless it's a super cooled super conductor.
Just like every switch will show some 'Bleed' when it's open.
Lubrication and ionized moisture will show some conductivity even when the switch contacts are open... | Ranging from not exactly to not even close.
You guys need to learn basic electricity. What it is and how it flows. The mysteries will become open to you.
I ain’t got time to help you right now. I get the granddaughter in the morning and until Sunday. My brother and sister-in-law are coming in from out of state on Sunday and staying until the 4th. I’ll be busy so that will give you time to learn the basics by the 5th and we can discuss it if you want.
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06-24-2009, 02:33 PM
|  | I Might Just Know What I'm Talking About | | Join Date: May 2003 Location: Nebraska
Posts: 1,687
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Quote: |
It's a switch, not a resistance! ANY resistance is unacceptable.
| That's right... STOP RESISTING!!
Sorry, I just couldn't "resist". 
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