veryhot_post in wiring harness meltdown.. in Electrical & Audio Author Topic: wiring harness meltdown..  (Read 3559 times)

Offline chargerdon

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xx in wiring harness meltdown.. in Electrical & Audio
wiring harness meltdown..
« on: July 14, 2018, 01:42:01 PM »
This is on my 74 Challenger...   difficult to get accurate wiring diagram for the 74...  Plus pretty sure mine had been messed with to bypass the federal seat belt interlock system.     

My problem started with an intermittent no crank.   Thought probably no ground from neutral safety switch, but, with voltmeter tested the ground at starter relay (when it didn't want to crank) and had ground.   Then tested the Start wire to the starter relay, and with wife hitting the starter...No Power.    So, i traced wire back to the right must bulk head connector and pulled it off...there was fair amount of corrosion...so note to myself to later take the time to clean each spade and each female connector on that bulkhead (wires 17-24)   I also re-pushed together the flat wiring connector at the steering wheel... Reconnected and tried and it cranked right over and started right up...  Problem solved...or so i thought.

Next morning, Decided to take it for a morning spin, and it cranked over but sputtered several times before starting...  ok..it sometimes doesn't like being cold ...especially with that hot cam in it...   pulled out of driveway and down my street...and it stalled when i came to stop sign..  Cranked...and it sputtered to life, but noticed smoke coming from under hood...and it stalled again...   left it off and opened hood and saw that i had burned the insulation off of a wire in the under hood wiring harness..  Shit...   so with help of the wife pushed it back to garage.. 

I ended up taking off the bulkhead wiring harness completely and taking into the house to replace the bad wires and clean completely all of the spades.  ( i also cleaned all of the female connectors with emory boards, and spray contact connector cleaner spray.  In repairing harness I replaced the wire which was completely destroyed is the one from bulkhead connector #23 which runs to the main distribution point which then feeds the choke heater, voltage regulator, ballast resistor, alternator field terminal, and one of the ecu power points. 

I also, then repaired any other wire showing damage, and continuity checked every bulkhead connector to its end point on the harness, as well as every one of the 5 leads in the ecu to their respective ends.   So, with all of the continuity checks being good, the harness should now be good !!   I think!!.

Re-installed and engine will crank, but no start...(it is definitely getting gas).   I've put on a timing light while cranking but it never lights so the ignition system isn't firing.   

With ignition on i have probed with multimeter and have power to the positive post on coil and onto all four posts on the ballast resistor.   I have tried swapping coil and ECU thinking maybe they got shorted out during the wire melt down...   Still no start...  PS the spare ECU i put on has never been tested...   but what are the odds of both the original and new after market ECU being bad?   

Thinking ok, so with ignition on i have power to the coil and ballast, but what about during cranking that uses post 22 on bulkhead connector?   to eliminate this as a problem i turned on the ignition (run position) and then make it crank by bypass wire at the starter relay...still no fire, and checking with timing light...NO LIGHT NO FIRE!! 

Suggestions on what to check next?   This being a factory electronic ignition, is there anything in the distributor itself that might be fried ?  Is there a bench check for the ECU ...   ?  Distributor? 

   



Linkback: https://forum.e-bodies.org/electrical-and-audio/11/wiring-harness-meltdown/7678/

Offline chargerdon

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Re: wiring harness meltdown..
« Reply #1 on: July 14, 2018, 06:18:43 PM »
CORRECTION...   If i turn the key to RUN not start and jumper the relay block to make it crank it will start !!   

Knowing this i then pulled off the start wire from the relay so engine wont crank, and also pulled BOTH ballast resistor connectors off.   With key in RUN i have power on the blue connector that jumps to the other side.   AND like .3 volt on the other ballast connector (the one that gets the start switch wire).    If i turn the key to Start then the power goes to zero on the RUN ballast connector and i get about 11 volt at the start ballast connector.    Sounds good...but with both connected on RUN i show 11.5 volt at the positive coil connector, but when i turn the key to start The voltage drops to zero at the coil positive connector.   No wonder it wont start...but why??   Do i have a short somewhere, or is the voltage i see on START connector phoney...i.e shows 11 volt but maybe no amperage??  i.e not passing enough current to run the coil and ecu ?   

Offline screamindriver

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Re: wiring harness meltdown..
« Reply #2 on: July 14, 2018, 09:15:08 PM »
I'd recheck and make sure the ignition switch connectors are clean..If they're black or corroded you'll have an intermittant problem.. It's the wide,flat one under the steering column{there's two one is the turn signal connector}...Is the seat belt switch bypass something that needs attention ???

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Re: wiring harness meltdown..
« Reply #2 on: July 14, 2018, 09:15:08 PM »

Offline chargerdon

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Re: wiring harness meltdown..
« Reply #3 on: July 16, 2018, 01:33:36 PM »
More tests...

Ran a wire from the starter relay positive cable to the brown wire on ballast (that is were the "start" wire makes firs contact).   Then turned engine over with key and it starts!!!!   So, i would say from that point on the harness and all components are good. 

Also, to verify that power is going thru (at least a little) i hooked up a DC 12 Volt motor i have that draws 2 amp...to the brown ballast wire with it disconnected from ballast...and turning key to start...it ran the motor fine!!   So at least two amps can go thru the start path...  Maybe that isn't enough or...why wouldn't it work all connected ?   


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Re: wiring harness meltdown..
« Reply #4 on: July 16, 2018, 01:36:45 PM »

Have you replaced the ballast resistor?
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Offline blown motor

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Re: wiring harness meltdown..
« Reply #5 on: July 16, 2018, 01:47:26 PM »
@chargerdon You can get an excellent laminated wiring diagram for your car here. https://www.classiccarwiring.com/challenger/
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Offline jimynick

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Re: wiring harness meltdown..
« Reply #6 on: July 16, 2018, 06:42:28 PM »
If you can figure out what particular part of the wiring may be your problem, I have an OEM 74 shop manual that I could scan the page and email to you, but there's probably over 50 pages of schematics in that manual. Just my  :alan2cents:
In the immortal words of Jimmy Scott- "pace yourself!"

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xx in wiring harness meltdown.. in Electrical & Audio
Re: wiring harness meltdown..
« Reply #6 on: July 16, 2018, 06:42:28 PM »

Offline chargerdon

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Re: wiring harness meltdown..
« Reply #7 on: July 20, 2018, 01:51:54 PM »
HPCuda
"Have you replaced the ballast resistor?"   

No i hadn't but i did run checks the resistance on the two sides, and it read 1.6 ohm on one side and 5.7 ohm on the other side.  So it looked correct.   I also have a spare and it reads the same OHM resistance. Also, one of my tests was to run a wire directly from positive post on battery and to the "backside" of the connector housing the "start" wire from bulkhead.   When i did this the car would then start on the key !!!   Of course i could shut key off and still have engine continue to run until i remove that wire.   So, based on this bulkhead/ignition key wire bypass and the OHMS resistance test, i concluded nothing wrong with the ballast resistor.

Well today in desperation, I replaced the ballast resistor with an old one i had as a spare.    So, because of the tests i really didn't expect any different results, but what the heck i have a spare and it only takes 5 mins to swap.   AND IT STARTED from the key...   5 times in a row...yippee...   However, i let the car sit for an hour...and went out to try again...and NO START unless i jump it at starter relay while in run, or run a bypass wire to the "start" wire on the ballast...   

This is so frustrating !!!!!!!!!!!!!!!!!!!!!!!   

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Re: wiring harness meltdown..
« Reply #8 on: July 20, 2018, 05:30:49 PM »
CORRECTION...   If i turn the key to RUN not start and jumper the relay block to make it crank it will start !!   

Knowing this i then pulled off the start wire from the relay so engine wont crank, and also pulled BOTH ballast resistor connectors off.   With key in RUN i have power on the blue connector that jumps to the other side.   AND like .3 volt on the other ballast connector (the one that gets the start switch wire).    If i turn the key to Start then the power goes to zero on the RUN ballast connector and i get about 11 volt at the start ballast connector.    Sounds good...but with both connected on RUN i show 11.5 volt at the positive coil connector, but when i turn the key to start The voltage drops to zero at the coil positive connector.   No wonder it wont start...but why??   Do i have a short somewhere, or is the voltage i see on START connector phoney...i.e shows 11 volt but maybe no amperage??  i.e not passing enough current to run the coil and ecu ?   

 You've got it! The reason is that you are using a volt meter, by nature they draw a VERY small amount of amperage. You can use it to test the ignition system but the circuit must be "loaded". There is an easier way however- use an old school test light probe for this test. They are available for cheap in any auto parts store. It looks like an ice pick with a bulb in it and a wire coming out of the handle. There is an alligator clip on the end of the wire. Attach the clip to a good ground and carefully insert the probe into the connector you want to test. Switch on the key and the bulb lights up loading the circuit for you indicating voltage and amperage.
  You have done some thorough testing already, nice job! I think you will find that you have high resistance on your Hot-On-Start wire (usually brown ). You have already proven this out by wiring to the start solenoid. Sorry for your frustration, I hope this helps! :bigthumb:

Offline chargerdon

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Re: wiring harness meltdown..
« Reply #9 on: July 21, 2018, 11:30:42 AM »
I have a test light, but that isn't good enough.   I.e. I tested my test light for amperage and it draws less than .1 amps for the light.   The ignition system draws between 5 and 6 amp.   So it can light up and still not be passing anywhere near enough current.. 

Offline 734406PK

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Re: wiring harness meltdown..
« Reply #10 on: July 21, 2018, 06:35:20 PM »
I have a test light, but that isn't good enough.   I.e. I tested my test light for amperage and it draws less than .1 amps for the light.   The ignition system draws between 5 and 6 amp.   So it can light up and still not be passing anywhere near enough current..

Ok then in that case, you can use a bulb with a larger amp draw like an 1156 or the "bright side" of an 1157. Another option is to use your volt meter with the circuit connected (loaded) to the start side of the ignition system. Disconnect the start relay so the engine won't crank, have someone hold the key switch in the "start" position. Check the voltage available at the ignition start circuit with the full 5-6 amp current flow.

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Re: wiring harness meltdown..
« Reply #10 on: July 21, 2018, 06:35:20 PM »

Offline chargerdon

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Re: wiring harness meltdown..
« Reply #11 on: July 22, 2018, 10:42:49 AM »
Ok....anybody know how difficult it is to replace the ignition switch wiring and harness??   Any body have instructions for this? 

1) do have to remove the steering wheel? 

2) how do you get the key lock mechanism out? 

The reason i ask is that today, I Tapped onto the brown wire that goes into the flat ignition connector, and ran this wire thru the firewall and into a tap i but on the brown wire (start wire) at the ballast resistor.   Then using the key switch tried to start the car, but, she would not start.   I then put my amp tester in line and when i try starting it is only reading about .6 amp.   I thought maybe most of the current is following the normal path thru the bulkhead connector...   i.e two paths..So...

i then removed that bypass and put my amp meter between the ballast resistor and the normal start wire and read about 2.5 amp...  so 2.5 and .5 is only 3 amp...   wish i knew what the minimum was to fire the coil and operate the ecu.   

Ok. so to prove to myself that i'm not all wet, i repeated putting a wire direct from battery post into the brown start  wire connector, and hit the key and she started...   Running it thru my amp gauge showed almost 11 amp...

Based upon this,  feed int starter wire directly from battery, car will start on key, but the bypass wire from take on ignition switch into its flat connector wont...   I am now believing that it isn't the wiring but the ignition switch itself is going bad. 

So... I see a new one on ebay for $33 not all that expensive...  but will need help figuring out how to replace it!   I have never taken a steering wheel apart.   

Does anyone agree with my conclusion...or should i still look elsewhere? 


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Re: wiring harness meltdown..
« Reply #12 on: July 22, 2018, 01:22:01 PM »
Do you have access to a spare column/switch? I'd plug one in before I would dig into the column & replace the switch.....  Also be aware the aftermarket switches are crap.... I'd source a original be it NOS or used long before I'd deal with an aftermarket switch... Way to much work to change it to put in a POS... 

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Re: wiring harness meltdown..
« Reply #13 on: July 22, 2018, 05:17:32 PM »
Do you have access to a spare column/switch? I'd plug one in before I would dig into the column & replace the switch.....  Also be aware the aftermarket switches are crap.... I'd source a original be it NOS or used long before I'd deal with an aftermarket switch... Way to much work to change it to put in a POS...

I agree! Most of the aftermarket stuff is crap, unfortunately. I had issues with a turn signal switch, brand new aftermarket, it was miswired at the flat connector. It cost me 3 hours of wtf? head scratching. I would suggest the same, look for NOS or even a Standard-Blue Streak option. I wound up getting a turn signal switch from YearOne,(Dave at Rosville would have been better)  worked just fine. I think you have found your problem anyway! Congrats!
« Last Edit: July 22, 2018, 06:49:08 PM by 734406PK »

Offline chargerdon

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Re: wiring harness meltdown..
« Reply #14 on: July 22, 2018, 06:07:21 PM »
Mmmm   No i don't have a spare switch...   tho if i buy a new one, it sure is a good idea to plug it into the harness before installing to see if it truly fixes the problem.   

Regarding OEM vs reproduction, first i do not see any oem switches on ebay or rock auto or any of the parts stores...their all aftermarket.   I do see two differences....   The illustrations for all of the switches i have found on ebay and rock auto...  all show a 8 pin connector but two of the connectors are empty making it a six wire system.   Mine is 8 wire !!    In addition the aftermarket all show wire 2 the black wire that goes to power the fuse panel, and the main power in red wire are not in the connector...so that you can bypass the flat connector...i suppose to cut down on heat in the flat connector.  Mine are in it...so i could push them in...  or pull out of other side and do a bypass of the connector for those two. 

b) The smaller wires 7 and 8 are not there at all !   I.e all of them are only 6 pin harness and connector.   My car has wires 7 and 8...   wiring diagram shows pin 8 black wire as going to the left door switch...  (i think for the ignition switch courtesy light which my car has and it does work...   and pin 7 has two orange wires ...one goes to a bus for the other interior lights... ash tray and glove box...  both of those are functional...  i this it was an order package i believe...   

So right off the bat the aftermarket switches are incomplete.  Because of this and the work involved, and not knowing for sure it that is the problem.........

I am soooo close to buying another starter relay for about $10...   giving it solid ground, power in from the main battery post on the existing starter relay,  the trigger wire tied to the current starter trigger wire on starter relay and the out would be strung to the ballast resister...   I think the starter start wire has enough power to trigger a this relay, that would send straight battery to the start wire on the ballast.   Hmmmm   Certainly not stock...but i think it would work...   Would be a lot cheaper and easier than replacing the starter ignition switch...especially if that didn't actually cure the problem.     

Two negatives...one not stock.... someday could cause me to lose a car show, and secondly if the ignition switch is at fault, then it might crap out completely later and need replacing anyways...   Hmmmmmmm

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xx in wiring harness meltdown.. in Electrical & Audio
Re: wiring harness meltdown..
« Reply #14 on: July 22, 2018, 06:07:21 PM »

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