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My '85 Honda Shadow VT700C has an issue I need help with... When the key is turned on the front turn signal lights illuminate as running lights, as they should. The rear ones do not illuminate. The license plate light and rear brake/tail lights function normally. When the left and right turn signals are used the front and rear turn signal lights function properly. The TAIL LIGHT warning light on the panel seemingly illuminates randomly. Any thoughts as to what the issue could be and how to fix it? Your feedback is greatly appreciated. Thanks!
 

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Begin by obtaining a schematic for your bike.

You may be able to find one on the Internet, as a .pdf, .gif or whatever.

Otherwise head down to the Honda dealer with your digital camera and take COLOR pictures of the schematic in their 1985 manual.

What? They don't have manuals that old anymore? Buy a 1985 manual on eBay for $29.

Preferably purchase a FACTORY manual. suggest you contact seller and CONFIRM that the schematic is still in it. Often they've been ripped out.

http://www.ebay.com/itm/1983-HONDA-VT750C-1984-1985-VT700C-OEM-Service-Manual-/191294458790

a Clymer like this would probably suffice

http://www.ebay.com/bhp/honda-vt-700-manual

Figure out what wire colors go where and THEN someone can help you diagnose your broken rear running lights and tail light warning lamp malfunctions.
 

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If I understand right, you front lights all work fine?

And the rear turn signals work, but not as tail lights?

Are they suppose to work as tail lights? Lets assume they do.
Replace both rear bulbs. Make sure you get the right one.
If you have NEVER seen the rear lights work, have someone look the correct bulb up to make sure you have the correct ones in there now, you would be surprised...

I agree with getting an electrical print, I am sure you can find one online.

As a rule Honda feeds +12vdc to a component and switches ground, that means your flashing lights on the dash could be a nicked wire finding ground.
I would look the cabling going to the neck over. But I would try new bulbs first.
 

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The first thing I would do is apply a good penetrant like PB Blaster or Freeze-Off is even better and available at O'Reilles. Do the light bulb socket on the signals and the tail light socket. Disconnect the bullet connectors leading to the rear of the bike and clean with penetrant as well. I have even sprayed Freeze-off into old Honda switches without dis-assembly and had them work again

Auto parts stores sell light bulb [silicone] grease that should be used on all those connections as well.

I would do all this first as a maintenance baseline, and then do as others have suggested. On the older bikes corrosion in the connectors and bulb sockets is a common problem.
 

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A lot of good comments on this thread that apply to electrical problems in general, and not just this specific bike.

Perhaps worth a few more words about "switched grounds."

Some bikes, and some cars, supply constant 12V to lights and turn them on and off by applying ground to complete the circuit.

So what are the benefits and downsides of this approach?

Well, if you have always hot (12V) wires all over a vehicle, and one of 'em chafes, the fuse instantly blows.

Compare this to switched hot, where the fuse doesn't blow UNTIL you turn on the lights, blinkers, whatever.

Well, when or why is this important? If you're diagnosing a blown fuse, would you prefer it to blow as soon as you put a new one in, or when you go and try and operate the circuit?

If they're switched hot you can at least ride the vehicle and NOT use that circuit to get to a repair shop, whatever.

Another thing. It's darned CONVENIENT to simply run the negative side of lights etc. to a chassis/frame ground connection-- usually just a ring terminal underneath a sheet metal screw.. You only have ONE wire to each taillight instead of two. So you use half as much wire, the wire harness is smaller, etc.

Except....as frame/body grounds get old, corrode, rust, your lights get dimmer and dimmer. You have to VOLTAGE DROP circuits to find those old corroded connections.

But...say you have a taillight mounted to a plastic fender...can't just stick a screw through it for a ground.

The main thing is you have to FIGURE OUT whether you have switched hot or switched ground lights, accessories, etc. and diagnose problems accordingly. In the end it's a big cup of "no big deal" which way they are wired.
 
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