Electrical Troubleshooting - not my forte - Brake Lights/Turn Signals

[gregwils]

"i think there is a crossed wire that has to do with the charging system for it to only blow with the engine running"

+1 My issues were slightly different, but I crossed the wires in a turn signal and created really erratic behavior. It was tough to figure out. The left turn signal was blowing even though the wires in the right turn signal were crossed. If T77's suggestion doesn't work, you may want to review every change you made even though they do not appear to be directly related.

[Joe Bob]

I agree...get a multimeter. I have two. One for travel and one for the home tool box.

On the lights, what wattage? If over 55w you likely need a relay kit once you fix the high resistance issue...that is if the meter confirms that.

Electricity, especially DC can be a head scratcher w/o the right diagnostic tools.

[JeremyD]

I did put in a relay kit - Sucro version. When I first got the car - the high beams were inop - the headlight/turn signal stalk switch was melted...

[JeremyD]

Pictures of the fuse box

[Bill in OKC]

Originally Posted by T77911S

unplug both LED lights. if the wires are shorting to ground, the LEDs will not make a difference. then try each one by itself. you could also put a MM in place of the fuse to measure current in all conditions, no leds, lft, rt, both. well, you dont need the MM with no led's, you just want to see if the fuse blows, but i am curious of the current of the LED's.

yup

[Jerry1]

JeremyD
I recently went through my 67 912 wiring and found at the floorboard area where the wiring harness spits off were the brake wires come out to the peddle. I had wires shorted out in that junction. You might try to peel the wiring harness insulation back and check the wires there. Mine were melted together. Not the funnest place to work in these cars just a suggestion.

[T77911S]

one pic i see heat shrink on one wire, another i it looks like 2 wires.

[JeremyD]

That was from the headlight relay kit.

My plan tonight is to replace the LED's and start troubleshooting to see what actually makes the fuse burn.

I'll start with the car engine "off" and the key in the "on" position and go from there.

[JeremyD]

OK - so this is where I am

Replaced the LED's with traditional bulbs

pulled the three wired out of the lower fuse panel and attached one at a time. First with just the ignition switch on - then if the fuse was not warm, turned the car on to see if the fuse warmed.

First wire was the driver's turn signal - tested great - so got a piece of blue tape.

Then tested the next wire - brake lights - tested great - even put the driving lights on

Then went to the third wire - and I am guessing this is where my problem lies.

EDIT : Looks like my reverse lights are grounding somewhere - NOT my turn signals



My tools


Should I reassemble all except the bad wire and take for a drive and see if I can get the fuse to blow?

[ossiblue]

Jeremy,

First, let me say I'm no expert on wiring but here's what I found so far from studying a 74 wiring diagram.

To keep things consistent, the diagram numbers the fuses from right to left, so #8 in your post is actually fuse #11 in the diagrams. I will use the numbering from the diagram from now on.

Fuse #11, which you have been testing, should have three wires--green/yellow, green/blue, and green/red. I cannot see the colors of all three in your picture, but I do see gr/yw, and gr/bl. Gr/yw should go to the back up light switch, gr/bl should go to the brake light switch, and gr/rd should go to the hazard switch.

The fuses for the turn signals and are #9 (right side) and #10 (left side). #9 should have two black/green entering and one exiting. #10 should have two black/white entering and one exiting. From your photo, that is correct (remember, move two fuses to the right from where you've been testing to get the correct fuse.)

Without going any further, it looks like there is some mis-wiring or misidentification. Again, I'm no expert but since there's been a lot of rewiring done on your car, it's certainly possible.

BTW, can you post the colors of the three wires you found on fuse #11 (your #8)?

[JeremyD]

OK - took a drive - with just my brake lights connected - thrashed the car around some and no issues - no burnt fuses.

Then came back and reattached the turn signal line - and after cleaning some of the connectors - my turn signals are working now too.

The only issue seems to be the reverse light. When I connected this wire there was an audible change in the speed of the fuel pump running - So I am guessing that this is where the resistance is coming from. I'm also guessing that because I started the car in reverse the other day which is why the fuse blew.

I'll try and drive with the rear reverse lights disconnected to see if this clears my problem.

[JeremyD]

The culprit - when I attached this line - big spark and audible change in the fuel pump

[Determined]

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