A Hot Time in the Ol' Fiero Tonight (Page 1/4)
Notorio JAN 29, 07:47 PM
NOTE: On Feb 5th I added what amounts to a second line of questioning, namely, has this harness been hacked (as warned of by Ogre.) So new pictures appear in a reply from Feb 5th where I removed the heat tape and conduit and found a surprise (but also an answer about the wire I had just melted).


Just got my 88 v6 5spd back together after 18 months. I ran the oil pump with a drill then got the final connections together for the long-awaited attempt to start up. While tightening the positive battery terminal the green wire indicated in the pictures started to melt away its insulation. With all due alacrity I got the battery disconnected while thanking my lucky stars that I didn't torch my baby (and garage, etc.) It looks like I have an appointment with the manual to discover where this green wire goes ... perhaps I somehow shorted it to ground? Any thoughts?

Close-up ...

[This message has been edited by Notorio (edited 02-05-2020).]

cvxjet JAN 29, 08:22 PM
Looking at my 88 manual wiring diagram, green from the C500 connector could be A) Air conditioning compressor, B) Coolant fan, C) Backup lights, or D) Cruise control...

You may want to pull fuses for your A/C, Cruise and Coolant fan, then connect the battery and see if you are still getting an voltage on that wire...Then install one fuse after another until it shows up....That would get you to which system is shorting.....

Is the wire just green, (Dark or light) or does it have a strip? (White or yellow)
fieroguru JAN 29, 09:07 PM
My money is on the backup lights - they are battery powered, not key on.

All AC functions go through the 203 connection and all cruise functions go through the C500, but are not in the engine side of the harness - they go around the back in the taillight portion of the harness.

Here is a modified copy of the C500 connection that has more detail than most.
Notorio JAN 29, 10:56 PM
Guys, thanks for the expert help!! I'll try what you suggested in the morning. As far as I can tell the melted wire is a light green, no trace. There are a couple darker green but it looks like they may have traces. I'm going to have to clean the grime off of these so I can get a better look.

Another clue ... this car does not have cruise control but did have A/C, which suffered the black death a few years ago. During this rebuild I left the compressor off and zip-tied the two A/C harnesses together off to the side so I could use them at some future time, if any, to get the air operational again. And I was hooking the battery up with the key off and out of the ignition.

[This message has been edited by Notorio (edited 01-29-2020).]

cvxjet JAN 29, 11:48 PM
I want to state here; Long ago, my father helped me install an aftermarket cruise control....We went in for lunch and when we came out an hour later, I happened to notice the plastic over the backup lights was bent in......We had left the key on and the shifter was in reverse....So those lights were on for an hour and MELTED the taillight backup lenses!

Never park the shifter in reverse....

(I just checked and my backup lights come on with the shifter in reverse- but the key OFF! Is that right? (I would think it would be "Key power")
Notorio JAN 30, 12:15 AM

Originally posted by cvxjet:
Never park the shifter in reverse....

What a bummer but great advice.

So here is the connector taken off. It is filled with a reflective, tar-like substance (?) so it is hard to see what is going on in the picture. On the front side of this male connector I have one side of my multimeter hooked to the bare copper wire where the insulation was melted away. On the bottom row, on the second small pin from the left in the picture at the tip of the red arrow, touching my other lead locks in the continuity buzzer and shows a resistance < 0.1 ohms. On the top row, on the second pin (large pin in this case) at the tip of the green arrow, touching my other lead beeps the continuity buzzer for just a moment and the resistance rapidly goes off scale.

Next step is to try to correlate the pins with assignments in the detailed diagram ...
Notorio JAN 30, 12:19 AM
Looks like the 'red arrow' with the direct connection to my melted wire is F9 = backup lights!! I'm going to ignore the 'green arrow' top pin for now. So, this means I've shorted the back-up wire somehow??
olejoedad JAN 30, 08:55 AM
No the red arrow points to A2 - Block Ground. The wire is sometimes Black, and sometimes Light Green.

The green arrow is indicating E2 - Solenoid Signal, Manual Trans.

As a note there is no wiring for the cruise control or the A/C that passes through the engine plug for the C500.
theogre JAN 30, 02:43 PM
Mark pins are on Engine side of C500.
C500 Light side is other side of bolt.
Remove pins. See my Cave, Terminal Access

Assuming Wiring is OE, not hacked doing engine swap etc...

Cooked Lt Grn in Engine side is likely BU light on C500 E1 (Think is One Left of Green Arrow)
Side Note: Fat black joint w/ "orange" weird wire at E3 next to cook wire is a Fusible Link for HEI. Do Not Cut/Damage this wire.

LT Grn wire Is Not connected to battery. Another wire and BU switch gets power first. They maybe have damage too.

if only cooked wire has Likely a short on body side of C500
or rest of BU lights are cooked but you haven't looked.

Look at body side etc for more cooked LtGrn wire. Likely need to unwrap engine harness to find/fix known damage.

C500 above isn't 88. This is...

Both from 88 Fiero FSM. Sim to 84 but not as bad... 88 has wiring changes vs earlier years and many things are different.
Note: C500 F10 wire colors maybe correct and GM authors of 88 Fiero FSM didn't update color on every other page. They make errors copy/past/edit pages many times in many FSM. Often didn't have data at time of change or simply cut cost making new FSM's every year.
Can use Circuit ID to follow most circuits. See my Cave, Wire Reading

[This message has been edited by theogre (edited 01-30-2020).]

Notorio JAN 30, 03:02 PM
Ogre, I didn't see your reply until after I tried something. I did misread the figure Olejoedad pointed out and immediately found a huge mistake on my part: the direct short of power to ground. Definitely a Doh! moment.

Above you can see I've got the green & black wire stake on connected to the positive terminal of the starter (!!!) So I removed that and attached it to the grounding lug towards the right side of the picture. This brought the resistance of the green-melted wire to < 1 ohm.

I decided to attempt a crank over with the coil plug pulled. When I climbed into the cabin I noticed the AJAR, and the BRAKES, VOLTS, and the OIL warning lights already on (at about half strength.) Turning the key to ON (but not CRANK) those lights brightened up to normal and several other lights came on. A brief crank shows the Starter and Tach are working. One additional issue: the fuel pump did not go on. I rechecked that and sure enough it was silent.

Status: Perhaps I've blown the Fuel Pump fuse but I can't account for the lights that are ON when the key is OFF.

[This message has been edited by Notorio (edited 01-30-2020).]