Electrical Problems Arrgh

Ngtflyr · #1 09-02-2009, 12:34 AM

Wondering if anyone has ran into this problem. 69 Z28, having an issue with the turnsignal fuse blowing. Only happens if the radio fuse is in (the one above the turnsignal fuse). With the radio fuse out, the turn signals operate normally, the 4 way flashers are on the fast side. I plan to replace the flasher and see if that fixes that issue (the fast 4 way flash). The one that has me perplexed is why does the fuse blow only when the other fuse from a totally seperate system is in.

Additional info: The dash wire harness, the fuse box, and the engine bay wire harness are all repro, the intermediary and trunk wire harnesses are original. thanks in advance

**njsteve** · #2 09-02-2009, 12:42 AM

Those cars are very sensitive to improper grounding. If you don't have the harnesses and the firewall to engine and radiator support to fenders grounded properly, the voltage will back feed into your harness and find another way to ground. That other way can be through other live circuits.

I found this out the hard way when I ended up frying my distributor points and block temp sender because I didn't have the engine to firewall, radiator support to subframe and engine to frame grounds hooked up.

You did mention that it is the neighboring fuse that is blowing so it might be feeding back through the nearest fused circuit. Check to see that you have your front fenders/radiator support grounded properly, and the dash ground wires hooked up.

Ngtflyr · #3 09-02-2009, 12:47 AM

Thanks Steve, I have been going thru all the grounds. That is usually the first place I go to when troubleshooting. I know I am missing the ground strap on the front passenger corner of the frame. Never was one there as far as I can determine. Also one of my firewall strap screw holes wallowed out and probably not making a good ground. thanks again

**Salvatore** · #4 09-02-2009, 01:47 AM

I also do NOT have a passenger side ground strap from frame to inner fender well. Never did. I have an early car maybe they came later? Kinda always wondered about that.

**William** · #5 09-02-2009, 02:49 AM

I believe early [maybe all] '69s had a ground strap as part of the steering coupler. Easy to leave off.

elonblock · #6 09-02-2009, 03:44 AM

Also make sure that the holes where the fastener attaches to the sheet metal are bare metal and have a good bite. And doesn't have a thin coating of paint insulating the grounding fastener.

This is critical especially if the car was touched up or restored in the engine bay with fresh paint.

It only takes a thin coating to insulate the fastener and seek a ground elsewhere as was mentioned previously.

I ended up welding up the holes in the firewall and redrilling, because the holes were oversized and the screws were basically a slip fit.

It can be a real hair puller!

Ngtflyr · #7 09-02-2009, 05:27 AM

I will be rechecking all the engine ground straps, and will be adding the ground strap to the passenger side frame to inner fender well. Looked at another car today that has one there. My car definitely never had one in that location but will tomorrow. All the ground straps are well illustrated on page 439 of the assembly manual as well. I will let you know if those fixes solve this PITA.

Ngtflyr · #8 09-24-2009, 12:27 AM

Well I am back on it after being gone a couple weeks for work. Still blowing the turn signal fuse, but only if the radio fuse (the one above the turn signal fuse) is in. If the radio fuse is out all is well. I have added an additional grounding strap that my car never had to the passenger front frame to inner fender well. Rechecked all the ground wires under the dash as well as the firewall and frame grounding straps. Replaced the flasher. If I unplug the radio wire harness the turn signal fuse still blows.

Feel like I am a dog chasing it's tail. I have noticed I hear a click under the dash somewhere about the same time the fuse blows.

**PxTx** · #9 09-24-2009, 05:14 AM

Sounds like you've got a dead short if there is a click just before the fuse blows. It has been a while since I've been through the wiring in these old cars. Is the cig lighter on the same circuit as the radio?

I would install the radio fuse and then grab a multi-meter. Put one lead on the negative batt terminal and start checking your leads on the turn signal circuit. Repeat on the radio circuit if nessisary.

You'll be looking for stray voltage. Ideally you'll have 12 volts on the positive terminals and 0 volts on the grounds. If there is less than 12 votls on a positive circuit or more than 0 volts on your grounds then I would look more closely in that direction.

Since it blows the fuse repeatedly you are actually in a good position. Figure with the radio fuse out, one of the power leads is just and open wire, fuse-in is providing power to the shorted area. The short is occuring when there is power being supplied to your turn signal ground(s) I suspect. Now that I type that, I'm thinking it's the other way around with the turn signal power shorting over on a radio ground, since it is the amps on the positive side which is blowing the fuse.

Again, I'm unclear in the specifics of these old harnesses. Can anyone else clarify things better? Am I going in the wrong direction?

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