Hello everyone, electrical and wiring experts your help is needed!

I have a 1988 Firbird Formula 5.0 litre TBI E code vin with 5 speed.

I was driving along and the car died, no power to the dash or ignition.

One of the fusible link wires at the starter is broken.

Closer inspection the other links were brittle and decided to replace them all.

After replacing and re-splicing in 4 new links, one wire is the cuplrit exhibiting a short condition.

Originally as in the picture GM had 2 wires, 12 & 14 guage joining into 1 16 guage link and 2 other fusible links at the starter junction, it is the bigger wire that is the cuplrit of the two that used to be joined by 1 fusible link and is shorted some where?

What is the bigger wire for that is causing the short and does it junction in anywhere, the harness go's into a thicker 3 way wiring tee up on top by the intake manifold and branches out in different directions from there.

Thanks

 

You've got a short on the main 12v feed to the fuseblock. Its discharging too much current for the link and it did its job of protecting the circuits by blowing. FWIW, its 10ga and the other two are 12ga

You will continue to blow links on that point until you track down and repair the short, be it faulty wiring, ground or dead solenoid somewhere stuck closed

 

Thanks Pocket, none of the wires were hooked to the starter during testing, I pulled the loom back up towards topside touched each wire one at a time with the test light probe connected to ground to ensure good connections after resplicing in the new fusible links.

I had the battery connected to positive and gator clipped a wire to the battery positive to each new wire splice and tested with the light probe.?

Here is another question?

Since that one larger wire in the picture is the only one arcing and is the main wire that goes back to the main fuse panel under the dash to test:

I pulled each fuse one by one and had a friend retouch the probe to the bad wire each time after the fuse was pulled it it still arced? up on topside not connected to the starter at all.

Can I conclude that the wire went bad somewhere before it goes back to the main fuse box in the dash.

I will have to proably pull that 10 guage wire out of the loom from the rest of the wires and look for a break or bad shield, contact, ground etc and follow it back to the main fuse block under the dash.

Thanks

 

Another question I have is the original fusible link in the picture in my 1st post the factory 2 into one that blew orginally is 16 guage, that is why I assumed the bigger wire was 12 guage and the smaller wire was 14.

I thought the fusible link general rule was, 4 guages higher then the lower number supported wire?

Thanks

 

I'm not sure about the fusible links, but don't even bother pulling the old wire out. Just "overlay" the wire. This literally is what it sounds like. Take a new wire, and run it along side the bad one. Just mark it at each end that the wire is shorted. I'd just make a tag of some sort so you don't get confused later on. You can even tuck your new wire into the loom and follow it the whole way. Just don't start yanking on the old wire though ... I see that causing more problems.

 

Good advice there. Just be sure you're overlaying the section containing the short and its been severed on both ends before tucking it away permanently. Id suggest investing $15 in a multimeter for any in depth electrical troubleshooting. The resistance function will be invaluable

Rule of thumb for links is 1/2 the wire size its protecting which is numerically 4 sizes higher

 

One of those wires goes to the cooling fan and A/C relays. May want to check or unplug those.

 

Thanks for the replys from everyone.

Below is a picture to the Mitchell repair wiring diagram, hopefully it is accurate.

I am following wiring diagram and the two into one fusible link shows:

1 red to high speed blower relay

1 red to a junction called A4 B/H (Body Harness)? and then on to ign/sw

I was hoping A4 was a junction and the bad part of the wire might be between where the starter contact is and A4 and not all the way back to the main fuse block in the dash.

I won't be able to get back to investigating and pulling and tracing the 1 bad culprit wire until this weekend!

 

Check the connector that goes to the high-speed blower relay - they get too hot and melt / get brittle over time. It's got the + feed and a negative which can touch. Located in a little sub-branch off the main loom at the back of the engine, on the pass side near the blower.

 

Thanks for the idea, I will inspect the blower relay first, before pulling the known bad 10 guage wire with the short out of the loom wrap to see where it goes.

 

I wasn't referring to the blower relay itself, though it would bear checking out. The connector that supplies power to the relay may be the problem. Read the following thread:

https://www.thirdgen.org/forums/elec...aro-rs-no.html

Post 5 has a nice colourful description of the connector and how to fix it. Post 14 has a nice colourful pic of the melted connector.

Don't know if this is your problem - only mentioning this cause it happened to me and left me stranded once - connector melted, shorted, and took out the fusible link.

 

Thank You very much!, appreciate the link to the information to the thread with the problem you experienced! I will investigate this area under the hood for sure to see if any thing looks suspect.

When it is finally resolved I will share my findings here so it may help others in the future.

Nothing more fustrating then having driven this vehicle for the last 15 years each summer season. The car has always been a fantastic runner and reliable up until now with this electrical problem.

 

A little bit of a update. Following Treefiddys suggestion, it appears that the black connector for the blower motor has overheated at some point, this may have caused my current problem, but I can not verify this for sure.

I seperated the locking black connector, tested the short condition on the suspect wire and it still has the short condition.

I then clipped the wires on the one side of the black connector from the harness feed figuring it would need to be replaced and hoping it was the cause of the short and retested the bad wire and the short condition is still there.

Is that black connector the resistor for the Blower/Heater motor and what can I replace it with at some point?

I have the bad wire traced from the loom on the passenger side and marked with the green tape in the picture, the only bad part is the loom continues toward the fire wall on the backside of the motor and has another y branch in the harness, which branched toward that loom with the burnt black connector and proably branches through the firewall to the main fuse panel.

 

The wires you snipped are for the HVAC fan inline connector, it simply unplugs

The resistor is a 4 pin unit bolted to the fiberglass box. Pull it out and you'll find several coils of wire exposed. Its near the fan relay

 

Thank You Pocket!

 

Didn't pan out, oh well. Hard to tell from the photo, but I assume you cut the wires from the loom side of the connector to remove it from the circuit and rule it out (obviously!).

Pretty much leaves the C100 connector thru the firewall, ign switch, fuse box, and the wiring in between. Next simplest things - pull the plug on the ign switch, and the PWR ACC breaker in the fuse box, see if the short goes. If not - pull the C100 connector (pita), see if you can isolate the short to engine bay or cabin.

 

Thanks TreeFiddy, after seeing the condition of the hvac connector, that is exactly what I did, was to cut it away from the main harness. I felt I had found the culprit, it was a little bit of a let down for sure that the short was still occuring on the wire.

I will investigate those other areas along with the C100 bulk head connector, for the ignition the PWR ACC fuse is 35 amps and metal and I did not pull that one in my fuse testing and there is another 35 amp called WDO?, not sure what wdo is for?.

Is the plug for the iginition switch in the column itself or under the dash by the main fuse panel.


Thanks for everyones help here on the board.

 

The other 35 amp circuit breaker (metal can) labeled WDO is for power windows.

I had that same connector burn out on me, but fortunately, removing it and splicing the wires together was all the fix I needed.

 

The PWR ACC breaker is fed directly by the wire that you have the short on. It runs the door locks, power seat, and demister. Possible your short could be one of these, so pull the breaker to rule them out.

The WDO power window breaker is fed from the ign switch in the run position only - won't be causing this problem. But easy enough to pull it out anyway and see - weird things do happen!

The ign switch is mounted up on top of the steering column, just above the pedals. You'll probably need to remove a few plastic panels to get to it. Big chunky connector with 2 interlocking parts.

 

Thanks, the car is a firebird formula edition and was not equipped with power windows or power door door locks.

The problem appears to be leaning more toward the ignition path, I will pull that ACC breaker.

Also in the HEI distributor, the ignition control module ICM, if that goes bad, can it cause a short condition? I know this has never been changed and is still the original ICM, only the cap and coil have been changed about 10 years ago.

Thanks again for the troubleshooting tips.

 

The ICM is only powered in ign run position, while your short is full-time. Won't be that.

 

Thanks for all the help and suggestions, at this time I am garageless and winter is setting in quickly, so I have preped the car for storage in the driveway for the season, but will be at it again in a few months and will post the resolution when I figure it out.

 

Update!, the car is up and running again.

The car was towed into a repair shop that specializes in electrical diagnosis and computer systems.

The fusible link that blew was for the heater and blower motor, the resistor for the blower motor was suspected as the problem.

The blower motor and resistor tested ok.

The problem was a bad or faulty ground, or lack of ground.

With all the testing and troubleshooting that I did, I never suspected bad or faulty ground as the culprit, I figured it was more along the lines of the positive or main ignition feed in that wire path.

When the main ground connection was lost, that is when one of the fusible links down by the starter went.

Thanks to all the help and trouble shooting tips here on the board from fellow members.

 

Don't really see how a bad ground was causing a short, cooked wiring, blown fusible links etc - usually that's the opposite symptoms - creating a high impedance or open circuit that won't allow power through at all

Anyway, glad to hear you finally got it fixed

 

Well I was going to pick up the car from the shop this week and it went belly up again, got a call from the shop today that the car was running fine multiple start ups and shutdowns last week after cleaning up the main ground and repairing the fusible links, they were testing after installing a new cruise/mutilfuntion switch, the new repaired fusible link for the main igintion feed went.

So it appears that there is intermintent short somewhere now that is coming and going to trace.

So now I wonder if could it be a faulty ignition switch or coil, the car has HEI? causing the intermintent short?

 

Just a update to the original problem on the 10 guage wire fusible link for the main ignition feed.

The on going short problem was traced to the C100 connection at the firewall where the 10 guage ignition feed wire passes through.

When the the wire originally blew the link, it caused damage to the plastic area in the C100 where the male/female meet.

That pin terminal connection was bypassed at the C100 for the 10 guage igintion feed wire.

A new piece of 10 guage wire was spliced in just before the C100 and passes through a factory rubber gromet hole close to the C100 feed.

The cars is up and running again, so thanks to all, who helped here on the forum.