70 chally electrical problem from hell!

[Relic]

Hey guys, I need some help. I just replaced all the wiring in my 70 challenger with M&H harnesses (except for the AC but that doesn't work yet anyway) and new bulbs. Also have a new alternator, new turn signal cam that goes in the column, and new flasher unit.

As of right now, I have valance panel lights working, and brights working but no headlights. Now when I turn on the brights, it sometimes kills the engine the second I do it. Once the the brights are on and the car is running, the passenger side fender turn indicator is stuck on but the the valence panel is still off.

I dont know what do think of this.

Next is the problem with the rear.
I have flashers on both sides but brakes lights only on the left side.

There is also a metal box that plugs into the old fuse box that wont plug into the M&H fuse box. I dont know what that box does but the plug layout on the new fuse box is completely different than the old on.
Ive been tearing my hair out over this for the past couple of weekends. Help???

[jimynick]

Jesus! I'd suggest posting lots of photos of the connections and connectors and calling M&H (who ever they are) for some help. Most aftermarket harnesses are clearly marked as to circuit and/or function. Make sure your grounds are clean and tight and numerous. 

[6packCuda]

The metal box that plugs in to the old fuse box might be the horn relay. Does the horn work?

[Canadian Cuda]

One thing that ive learned with all electrical is always make sure you have a really good ground where ever necessary

[Giveitawack]

I also bought M&H harnesses to my Barracuda -70.
The fuse box is for 71-74 according to YearOne. The metal box is the horn relay, provided with the harness.
I took the wiring diagram, the harnesses, a roll of masking tape and a marker pen to the living room and followed every wire and connection, marked where everething connected. Then put them in the car and it worked on the first try.
My impression of the M&H harnesses is that they look good and work fine, but even M&H can have a bad day...

[Relic]

I did try running a jumper ground wire to the rear taillights an it worked wonders for brightness. I still had brake lights on the left only though. Ill try cleaning up all my grounds today. Ive used M&H before in my 68 charger and had no problems which is why Im stumped as to whats going on here.
I checked the back of the old fuse block and that metal box is the horn relay. The plugs are still wrong for the new fuse block though so I guess I should call M&H on that.

Could a bad ground be my no headlight/half brake light problem??

[Jesus H Chrysler]

I would try to isolate each circuit and diagnose one at a time.  that means pulling all fuses except what you're working on at the time.  I've had some cars that were pretty hacked in the wiring department.  (Front parking lights were wired as brake lights, horn and wipers crossed etc).  This is the best method.  Start with headlights and disconnect everything else.  Then trace out and double check your wires.  Find where the problems are (usually cross connections or ground)  Once that is done then move on to front markers, rear brake etc.  Use a methodical approach one circuit at a time till you get the bugs out.

The reason to pull fuses and isolate the circuits is sometimes wires get crossed and end up backfeeding power where it shouldn't be.  That's why I had front brake lights on one truck.  Take the time and think it through and you should be fine.  Good luck!

[Relic]

Ok I pulled all the fuses except for the 20 amp one for brakes. I also made a ground wire for each lightbulb and made sure it had bare metal to ground too. Same problem, only left side brake lights.
 

Im going to make a video of all my connections and tests to see if there's something obvious I'm missing because Im really lost as to what the problem might be haha.

[Jesus H Chrysler]

Do you have a multimeter or test light?  Start tracing your wires back from the lights toward the fuse box.  Make sure its the right wire, color etc. not switched with another wire.  Say for example left brake is brown and right brake is yellow and markers are white.  Make sure those are properly connected at the fuse box, not swapped with another circuit.

Then make sure you have power from the fuse all the way to the light socket.  If you have the pointy style probes or test light you can poke through the insulation at various points to look for broken or pinched wires.

DIY systems are great for setting up the car the way you want, they just require a ton of planning and notes to make sure it's all right.

[ShelbyDogg]

Use a test light and probe the back of the turn signal connector at the steeing column connector. Do not unplug it yet.

Probe the brown wire (2nd down from the round end) light should come on for the right rear brake or flash for the right turn signal.
Probe the dark green wire (3rd down from the round end) light should come on for the left rear brake or flash for the left turn signal.
Probe the tan wire (6th down from the round end) light should come on and flash for the right front turn signal.
Probe the light green wire (7th down from the round end) light should come on and flash for the left front turn signal.

If you DON't have all 4 signals above, your turn signal switch is bad. (this is assuming that you have power coming in from the flasher or brake switch circuits.
If you DO have all 4, then you have to follow the 4 wires to the connectors, then to the sockets. The rear connector is by the parking brake pedal and the front connector is at the bulkhead with the headlight wires.

You could unplug the connector and run a FUSED hot wire to these wires, one at a time to troubleshoot the lights.  Jumper the body side connector and not the switch connector.

I would match all of the colors from the new fusebox and old box. There can't be one for all 71-74s. Some of those wires are switched around and moved for the different years. An example would be the horn wire for a 71 compared to a horn wire for a 72-74. You just can't plug it in without moving wires around.


 

[Giveitawack]

I had a strange phenomenon last week. I had installed new LED bulbs in the front park/turn signals. (Barracuda -70) Seemed to work fine.
I then started the engine and went for a drive. When I got back home I did a check with turn signals with the engine and Road Lamps on. Disco Light Show.The turn signals flashed, Road Lamps flashed, rear lights dimmed with each flash.
Changed back to the old bulbs in the front. Everything OK.
I guess the new LEDs were not assembled correctly from the factory. Haven't figured out what actually happened. Some kind of short or ground through the system.
What I am trying to say here is that maybe it is some bulb somewhere that is causing the problem.

[MEK-Dangerfield]

I had a strange phenomenon last week. I had installed new LED bulbs in the front park/turn signals. (Barracuda -70) Seemed to work fine.
I then started the engine and went for a drive. When I got back home I did a check with turn signals with the engine and Road Lamps on. Disco Light Show.The turn signals flashed, Road Lamps flashed, rear lights dimmed with each flash.
Changed back to the old bulbs in the front. Everything OK.
I guess the new LEDs were not assembled correctly from the factory. Haven't figured out what actually happened. Some kind of short or ground through the system.
What I am trying to say here is that maybe it is some bulb somewhere that is causing the problem.

Did you change out the turn signal flasher? LED's aren't enough of a load to get the old flashers to work. Mine wouldn't flash at all though. Maybe this will help you, maybe not.   

[ShelbyDogg]

I had a strange phenomenon last week. I had installed new LED bulbs in the front park/turn signals.I guess the new LEDs were not assembled correctly from the factory. Haven't figured out what actually happened. Some kind of short or ground through the system.
What I am trying to say here is that maybe it is some bulb somewhere that is causing the problem.

First, make sure that you have a good ground by using a jumper cable on the back of the bulb socket and the negative post of the battery. See if you still have your "disco light show"

I have those 1 dollar, 60 LED bulbs in my parking/turn signals too, in my 71 Challenger but haven't put it on the road yet. I just checked that they came on and got brighter when the turn signals flashed.  I like the way they look and will have to modify the base to work in my 4 taillights.   If you are getting a ground feedback through the LED bulbs, get a pack of cheap 1 amp diodes from radio shack, then install one at each wire going to the front light. Both stripes on the diodes should be towards the bulb side.  Make a small pig tail connector with these in the middle to try it. That way you can remove them by just plugging the connectors back together.

[Giveitawack]

Yes I have a LED flasher. Will change the Hazard relay too.
I now have three different 1157 LEDs I can try. The old LEDs work fine but they only light forward, not to the sides. The 60 SMD LEDs would have been cool, but they didn't work that well. But I have a third model that I will try.

[ShelbyDogg]

My 60 LED bulbs don't go down far enough into the tail light sockets so that I can lock them in.  The LEDs at the bottom hit the tabs that lockitinto the tail light housing.  Does your type lock in?  Your looks a little slimmer. I'll modify my base so that I can get them locked in.