[japrinten]

I'm installing a Painless 20121 complete wiring harness in my '68 vert and am having problems with fuses blowing for the turn signal circuits as soon as I turn the key.

A little background/context:

I installed the harness a couple of months ago and started testing the systems. Everything seemed to work fine- turn signals, rear back-up lights, engine cranked, etc - and then I tried the high beams. BAM! Both headlights blew out, necessitating replacement of the high beam switch. By this time I was so fed-up with working on the electrical system I switched to other tasks (more on the "Painless" installation in a separate posting… ).

Fast forward to this weekend and getting the electrical system sorted out is the only thing that is in the way of getting this project mobile for the first time in 7 years. Everything now checks out fine, with the exception of the turn signals. The rear lights work fine when the headlights are on or when applying the brakes, but as soon as I turn the key to power the system, the fuse for the turn signals/back-up blows. Also, activating the emergency flashers causes that fuse to blow after 2-3 seconds.

Since this is my first project involving a re-wire, I'm looking for some advice from the electrical gurus out there on how to go about troubleshooting and locating the issue.

BTW, check out Smart Glow fuses- really handy as they glow when blown.

 

[Greg'66 5.0]

If the fuses are blowing immediately upon power-up, that would indicate that you have a hard short to ground. If you have a multimeter, you can troubleshoot without wasting as many fuses. Remove the bulbs from the light housings so that you don't get erroneous readings from measuring through the bulb filaments. If you have incandescent bulbs for the turn signal indicators in your instrument panel, you'll need to remove those as well. Measure the resistance from the load side of the fuse to a body ground - you shouldn't see any continuity. If you have close to 0 ohms, you've got a short to ground. Disconnect both front & rear light housings from the wiring harness by pulling the plugs near the light housings and repeat the measurement. If the ground goes away, plug the light housings in one by one and check the resistance after connecting each one. When the zero ohm measurement returns, you've found where the short is. If you still see zero ohms with all the light housings disconnected, the short is somewhere on the harness. Since the brake lights share the same wiring with the rear turn signals, your problem could be in the brake light circuit. The brake light circuit gets power from a different fuse, so if that fuse doesn't normally blow when you stop on the brake pedal, you can eliminate your rear light housings as a source of the ground. If the fuse doesn't blow with brake lights and only blows when you try to use the turn signals, the problem is probably with the front signals.

For what it's worth, I ran into a similar problem when I first wired up my car. I don't have a wiring diagram handy so I don't know the differences between '66 and '68, but one thing I found is that wiring colors on the front turn signal/parking lights don't follow conventional automotive wiring colors. My repro light housings had 3 wires - black, brown, and blue. The mistake I made was that I assumed the black wire was the ground - it's really the brown wire that is the ground. When I connected my parking light wire to the brown wire, I inadvertently created a dead short. Once I switched the wires to what they should be, the problem went away.

 

[Chipster]

That's great advice!

 

[japrinten]

Greg-

Thanks for the great suggestions- although I probably saved $20 in fuses by going with the mulitmeter, the problem is persisting. I spend a couple of hours this morning troubleshooting:

- Load side of working circuits indeed registered 1, while both the E-Flasher and Turn Signals were at 0 ohms, so this confirms your suspicion of a hard short to ground (I removed bulbs from dash turn signals and the sidelights prior)

- Even after disconnecting the parking lights and the sidelights, the multimeter still reads 0 ohms, so it appears that the short may be in the harness. Before I start digging into the harness, are there places I should look first?

The funny thing about this is that the turn signals worked fine before the headlight blow-out- (I installed sequential turn lights and was delighted to see that they actually worked!). Could transient spike in current cause a grounding short elsewhere?

Thanks again!

 

[Greg'66 5.0]

Disconnect the turn signal switch connector at the steering column and try it again. The wires running through the column can chafe and end up shorting to ground. I would disconnect whatever connectors I could and measure the resistance in each portion of the circuit. At some point you should find a ground on one side but not on the other. Check your harness routing carefully and make sure the harness isn't running over any sharp edges that could cause chafing.

The spike in current that you had could have caused problems if things weren't grounded correctly. Electricity will always try to find a path to ground, even if that means running backwards through other circuits and eventually finding a ground. Taillight/parking light/turn signal circuits are usually the worst since they share different portions of the circuits.

 

[japrinten]

Thanks Greg- I was pondering this over lunch and was thinking the column was the next place to look. I believe the first time I had just the turn switch hooked up since the column wasn't installed yet.

Have to figure this out soon, since this will be occupying my mind until it's fixed!

 

[japrinten]

Blowing Fuses with Re-wire- Resolution

Thought I would close the loop on this issue. After completely dissassembling the front wiring harness (headlights, markers and turn signals) AND cleaning up the turn signal switch in the column AND replacing the flasher, the problem has been resolved.

It turns out that I had incorrectly re-attached a wire to ground at the front left turn signal when I had removed the lower valence earlier. Covering all of the the wires with PowerBraid made it not-so-obvious! The switch needed a bit of clean-up to be functional and the power surge from the faulty dimmer switch fried the LED flasher for my sequential tail lights. A call to Larry at ClassicLEDs and a new sequential LED set-up is in the mail.

Thanks again for all the advice!

 

[Rudedog289]

Solid posting, soon I will be installing a new harness in my 66 and this gives me plenty info to consider. Thanks

 

[japrinten]

Rudedog289- Which harness manufacturer did you go with? If you haven't purchased already, I can share my experiances (positive and negative) with the Painless Harness.