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Rear Harness Short

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bcbennett

bcbennett

Senior Member
Offline
Hi all,

Regarding my '74 TR6:

The fuse protecting marker, parking, brake, and dash lamps keeps blowing (red/green wire to double red wires). I removed each lamp, one at a time, no help. I have examined all connections, all seem fine. When I flip the light main switch, I get about ten seconds before the fuse blows, during which time all my back lamps are dark. The license plate lamps glow faintly.

However, the circuit hooked to my driver's rear marker lamp (double red wire to socket) is hot to the touch each time I flip the switch. Removing the lamp and removing the socket from the hole does not stop the wires from heating up, and even removing the lampholder from the spade connector does not stop the wires from heating. None of the other wires gets hot.

Thoughts?
 
Just a silly thought: could the main lighting switch itself be at fault?

UPDATE: Oops! I misread the part about the one wire getting hot. Perhaps you've a pinched and now-bare wire grounding out in the harness to the rear lamps. Given that it tends to run under carpeting and through various holes and passageways, there's ample opportunity for insulation to get worn off or even a wire partially cut and exposed.
 
I don't remember, is the license plate lamps outside the body on the 6? If so I would look where they go through the body. If so I bet the grommet has torn.

Other wise you start by disconnecting all the splices in the rear, and starting at the one closes to the switch, start reconnecting them until one sparks and blows the fuse.

There's a wire leaking electrons somewhere. I think the hot wires shows it's downstream of the side marker.
 
I would say you have two problems, both a poor connection at the spade connector for the marker lamp, and a short somewhere farther down the line from that point. As noted, the wires to the license lamp(s) are a likely suspect.

If you can't find the short through visual inspection, there are a couple of tricks that may help. One is to connect an old headlight bulb in place of the fuse, so that you can keep the circuit powered without blowing a fuse. The bulb doubles as an indication of when the short is removed.

Then with the bulb supplying current, you can also use a magnetic compass as a "current detector". When it gets close to a wire carrying current, the needle should deflect to align with the wire's magnetic field instead of the earth's magnetic field.
 
Have a look inside the rear license bulb holders. Over the years I have found everything from JB Weld and chewing gum holding these things together. Lucky you it's not burning up a light green wire or two.

Wayne
 
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