What us the name of the harness of wire at pins 1-12 on the engine compartment relay board? It melted last night, No sparks, just a lot of smoke.
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I pulled the plug and found what looks like a wire jump twisted between pins 7,9 and 11. Why would someone do that?
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The wires are toast. What is the sop repair? Undo the loom and replace each wire? The cap to the wire plug had come apart long ago. Any sources for the plug or the correct gauge/color wires?
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Yes, un-sleeve the wires and replace them.

There was a looped wire in the fuel pump circuit, so that may be what you're seeing. Check the wiring diagrams (in Haynes, or on Pelican) for details.

--DD

Nasty one.

Jeff B. can answer these questions I assume.

His site:

http://bowlsby.net/914/WiringHarnesses/

Jeff's email: jeff.bowlsby@sbcglobal.net

Good Luck.

--Wingnut86

You could just look at the wiring diagram, which is readily available online at Pelican Parts' website.

The Cap'n

Pin 7 is key hot from ignition sw. on. Pin 9 goes to the fuel pump fuse, and pin 11 goes to pin87 of the heater fan relay. Why someone would do that is beyond me?? Pin 85 of the heater fan relay is already hot from the trace from pin 8 of the 14 pin connector and also connects pin7 of the 12 pin connector to hot, which is the coil+. You should check out that 14 pin relay also. Sounds like a previous owner had problems and a misunderstanding of electrics.
Tom

Tom, Thanks, that's the info I hoped for. Your a champ.
I have al mess in my engine compartment today and you've helped me begin to sort it out.
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Electric problems stink (PI) I often second guess my own interpretation of a WD, and a little feedback helps tremendously.

I appreciate the link. Thanks very much.

Cap'n,

I have WD's, but I couldn't determine from these the correct description of that sheaf of wires emanating from terminals 1-12 on the engine relay board. I want to know because I have to replace both the harness and the plugs. Maybe its "the wires from pins 1-12 of the relay board." Maybe its called something else?

Also, I thought someone who can ID the jumped pins from memory might take mercy on me and communicate their function. I've mistakenly traced circuits in the past and these seemed obvious so it didn't hurt to ask.

Finally, just in case there was a valid reason for that procedure, I hoped someone might offer an opinion about the purpose of the illicit jump (e.g., "this is a common fix for X", or, as it turns out, "the PO probably didn't know what he/she was doing).

I'd appreciate any feedback.

Good used harness.

Here's a link to a relay board diagram:

http://www.pelicanparts.com/914/parts/Elec...lectric_73E.jpg


Note that pins 10 and 12 of the 12-pin connector have a line between them. On my car, that line is a green wire. That takes the output of the heater blower relay (pin 87 on the relay) and sends it to the blower (pin 11 on the 14-pin connector).

Sorry, I had thought it was in the pump circuit, but I was wrong.

--DD

One correction. Pin 9 goes to the heater fan fuse, fused side. The harness you have a problem with is the ignition harness. I'm sure Jeff has them, don't know the cost, but before you hook up another harness, find out why this one heated to the point of smoking.
I'm looking at the schematic for the relay board for a 73 year model. If yours is another year there may be some additional wires, but these 7 wires seem to be the same on all relay boards.
pins 2 and 4 both grey/brown are for the back up switch at the trans.
pin 1 is green/red for the oil pressure.
pin 6 is yellow for the starter solenoid.
pin 5 is black/purple for the tach signal.
pin 7 is black/red for coil +.
pin12 is white for AAR power.
Hope this helps.
I'm thinking you need to closely check that 14 pin connector out at the front of the relay board. Don't want to fry another harness, right?
I would probably leave the ignition harness off and turn the key to on and check the 12 pin for power at two pins 5 for coil and 12 for AAR. Also have someone turn to start and measure for power at pin 6 solenoid power. Measure with voltmeter from pin to ground.
If these are good, then something on the engine, AAR or coil, or one of the wires shorted to ground to cause the burned wires. Coil terminals have a tendency to do that.
Tom

PS: For Dave, that's pins 11 and 10 that are jumpered at the 12 pin connector. Pin 12 is power to AAR.

Obviously it's resistance, but what can cause a wire get so hot that the insulation burns off?

I think of loose terminals, two wires with bare spots shorting against each other, or a current back feeding from a shorted circuited component. The wires melted in the middle of their runs . Does that fact provide any clues?





McMark, So it's called s a "good used harness?" Just kidding. If you can source either new or used I'm in. I'm sending a PM.

Tom wrote:

"[B]efore you hook up another harness, find out why this one heated to the point of smoking....I'm thinking you need to closely check that 14 pin connector out at the front of the relay board."

Agreed. I'll follow the diagnostic procedure you thoughtfully provided and report back if I find anything of general interest. Something must have motivated the PO to jump pins and I'd like to know what even if that was not the right fix. Thanks again, you are a star.

Dave: Thanks for the updated info. Tracing electric problem is lonely work. I would have been lost dozens of times but for the P.P. schematics. For the record, my car is a '72, but after glancing through the diagrams it seems the relay board remains pretty consistent through the years.

Let me know if I can help you with a new harness, but you should try and figure out what caused the damage...was it a problem with the harness or something the harness was connected to? I sure dont like the looks of that rube goldberg wire on the relay board, thats not right.

You'll need an ignition harness...you'll save $25 if your core is rebuildable...

"rube goldberg wire on the relay"

I'm having trouble imagining what it was supposed to fix...

PM sent

D'OH!!

--DD

...I just received a box of cables from Jeff. Even the "good used one" is better than any of my cars ever saw with their previous owners.

Correction, my new 76' roller purchase probably has great cables under all the red paint and tape. But I tire of reworking cable ends after all that crap is removed...

Good luck..

Me too, that wire looks like problems. No PM received, you can email me from my website or using the email address above.

I've been told that 72 ignition wiring is a one-year version. Don't know if that affects the twelve-pin connection wiring or not. Pelican doesn't provide that year, and what I see is not entirely consistent with the Haynes schematic.

Be that as it may, I performed the tests Tom suggested at the Twelve-pin board, with the ignition harness detached:

Key on: pins 1 and 2, 7(coil positive), and 9 (blower) are energized.

Pin 12 (connects with the white AAR wire) is cold when key is on.

With the key in start position, Pin 6 (starter solenoid) is energized.

The burnt wires were #12 (AAR) and #4 (one of the two grey/brown back-up switches.)

The wiring around the back-up switch is unharmed.

I can't tell if there's any opportunity for 12 and 4 to short in the relay board circuits. The BW schematic in Haynes is too faded.

My inexperienced guess is that the hot lead in the AAR electric system caught the ground somehow. I have no idea why this also manifested by burning up part of the #4 wire.

BTW, according to my best reading of the schematic, 9 and 11 are associated with the heater fan. Thinking the blower didn't have power,the PO jumpered 7, 9, and 11, in a misguided attempt to get juice to the blower. The blower motor shows continuity between its leads so I assume its fried and that's the real reason it wouldn't turn on.

Thanks to everyone who've been helping me. Your input has been invaluable.

Stuart,
Looking closer, the AAR is only hot when the fuel pump relay is energized.
It sure looks like your wire to the AAR shorted to ground somewhere after leaving the relay board. As it heated up and melted the insulation, it melted the backup light wire also. When it melted it enough it just saw that wire as another path to ground, thru the back up light. If you can't find a place where the AAR wire shorted, maybe at the connector at the AAR, then I suppose the AAR itself may have gone bad. Might be a good idea to remove and test it on the bench.
Tom

"As it heated up and melted the insulation, it melted the backup light wire also."

It must be as you say since the BU wire insulation was intact for most of its length while the AAR wire was completely "skinned."

I'll check #12 with key on, then continuity of AAR. If those seem ok I'll rig a temporary harness and see what happens.

Thanks again, Tom.

Pin 12 will not be hot unless the fuel pump relay is energized and this only happems for 1.5 seconds when you first turn the key on, when the starter is engaged, or the engine is running. I don't think there is a problem with pin 12 not having power, as the wire melted before. Just need to be sure why before hooking up another harness. Running a temporary wire would be a good test. You will have to jumper the fuel pump relay ( remove relay and jumper pin 30 to pin 87) to do that with the rest of the harness removed.
Hey, you're welcome for the help, that what this forum is for, and I enjoy helping.
Tom