Wire, Wire, Pants on Fire

Warning! Before attempting any electrical repairs you must disconnect the battery. Capacitor banks in cars with large sound systems must be discharged. Failure to do this can result in fire and/or explosion hazards.

When you disconnect the battery, always take off the ground(s) first. The reason is that if your tool contacts the car body and negative terminal, you won't cause a short. If you do the positive first, and hit the body or block, you'll throw one hell of a spark. That spark can cause a power surge in the car that can do serious damage.

Discharging capacitors varies some depending on how they were installed. The easiest way is probably to turn on whatever they are connected to. Be very careful with these. Capacitors can dump huge amounts of power in a very short pulse that can easily weld things. Check them with a voltmeter to make sure they are flat before starting work.

Good Wire Hunting.

Several of us keep telling people in the forums to check the various wires in the car.... Here's a list of common things to check and some of what is going on with them. These things should be checked anytime you experience erratic or intermittent performance problems. (Unstable Idle is caused by electrical problems almost as much as vacuum or timing problems.)

Another factor often forgotten is that Fiero's engine bay is more exposed to weather than FWD cars using the same engines. Because of the vent grates, weather gets to the parts in there even when the car is parked. In most FWD models, the engine is much more protected by the hood and really only allows weather in the engine bay when the car is in use. This difference means Fiero often suffers from accelerated corrosion of electrical connections. (In this case, the term Weather would include things like car washing and anything else that dumps water down the vent grates.)

Note: While this article is written for GM cars and light trucks, it can be applied to most cars and trucks. ECM/PCM controlled vehicles are very fussy about charging system conditions. Corrosion of just one joint can throw the whole car out of whack.

Fusible Links

WARNING! Fusible links are calibrated wire with special insulation. Do Not replace them with normal wire. Fuse links are calculated to specific wire size and length. Do Not splice fusible links! Do Not cut them! If a fuse link needs a new end, it must be replaced. Do Not solder them!

Fuse Links blows mainly because:

Something is shorting out the battery or maybe the Alt
OE FL end(s) are bad and letting water etc at the wire
You/shop did a crap job to replace them and letting water etc at the wire, has loose crimps, etc.

The problem is you can't be 100% sure what caused it to fail unless you load test the circuit. Should you bypass a fuse link to get going on the road, pay careful attention to the car afterwards. If it failed because of a short, then you can have a bonfire on your hands real quick. Make sure you replace the dead link ASAP.

Alternator Fuse Links is not to protect the alt... Alt can short out and when that happens draws 300-400 amps from battery. Same as other Fuse Links. Even ECM standby power has a Fuse Link for this reason.

The ugly details on fuse links.

Why a fuse link and not a cartridge fuse or circuit breaker?

Fuse links are used in high current circuits like the battery and alternator outputs. They handle much greater current than normal automotive fuses and breakers. Fuse link circuits commonly carry 30-100 amps or more.

Most automotive breakers are automatic reset and that is undesirable on circuits that can easily start fires. Even if you eliminate auto reset, the increased cost during manufacture isn't justified for something that isn't as reliable as the fuse link.

Fuse links accept higher surge currents without blowing. This is important for things like the coolant fan motor, which draws high current at startup.

Delinking

Allot of questions come up about replacing fuse links with various other types of fuse. Generally this is a bad idea and if you do it wrong either you'll blow fuses when you shouldn't or you'll burn the car down because a fuse didn't blow that should have. Don't second-guess the carmakers on this. Unless you know exactly what you are doing this is a very dangerous thing to mess with.

One example, the alternator circuit... Allot of people don't understand why this circuit is fused and/or why it is always fused at a value that seems insanely high.

The alternator link/fuse is typically rated 100 amps or more depending on the alternator and vehicle options. But I only have a 60 to 90-amp alternator. That's true but the link/fuse is almost always sized to be able to carry the entire output of the alternator and then some. You will almost never see an alternator fuse fail from overloading the alternator. (You will however probably kill the alternator.)

Many people mistakenly think this link/fuse is to protect the alternator. Dumb as it first sounds, the fuse isn't there to protect the alternator at all. It protects the car from a short in the alternator or wiring to it. Such a short could potentially pull hundreds of amps from the battery, likely starting a fire, if the alternator circuit is left unprotected. The alternator would never directly blow that fuse but the current from a shorted battery would fry even a 200-amp fuse instantly.

ECM power

People forget to check fuses so often it's really sad. Whenever you suspect an ECM ignition or fuel system problem, this should be the first thing checked. All too often one of the multiple fuses for these items is popped and no one has looked here before chasing down the rest of the system.

How many fuses are involved? It varies depending on motor and year.

On the V6 Fiero there are,

The main ECM fuse.
The Fuse Link that provides memory power to the ECM.
Two 5 amp Fuel Injector fuses, one for each set of 3 injectors.
According to schematics, there is also a fuse link for the ignition coil.

The distributor 4 cylinder is the same for the ECM and coil but does away with the injector fuses. The single injector is fed from the 10-amp ECM fuse.

The DIS 4 cylinder has the injector, ignition brick, and ECM all sharing the same 10-amp fuse. The ECM still gets memory power from a fuse link.

Battery Cables

Warning! The OE routing of the positive battery cable is at best poorly done in many Fiero. As a result, the pulleys and belts can easily damage the cable. This cable MUST be physically inspected and replaced if there is any damage.

For 87-88 L4, and likely the earlier years, the cable is factory routed between the water pump and pulley. Even if all the cable clips etc are perfect, the cable has enough slack to easily reach the water pump pulley. In many cases, the cable may rub only under certain engine load conditions.

One giveaway that you've got problems here is to inspect the pump side of the pulley. If the cable is shorting against the pulley there will likely be rub and even burn marks on the edge of the pulley.

V6 owners aren't immune to this problem. The extremely cramped V6 setup makes checking the cable harder while making the cable easier to damage.

When replacing cables, use whatever routing will get the cable away from the pulleys and exhaust. I ran mine over the water pump on the L4. (If you have the V5 AC compressor, loop it under the diagonal compressor brace.) Now it is easy to visually inspect the cable and it is far from the pulleys and exhaust.

General Notes

Think weak battery? Test/replace battery and Replace, at least test, battery cables at same time. Weak cables are high on the list of screwing up starters.

These obviously need to be clean and tight on the battery but most people forget or don't know to check the other ends as well. There are several ends involved and all need to be in good shape or you will have problems. Often the problems can make you look in all the wrong directions. Things like poor engine performance and rough idle can often be traced to batty cables and charging system problems.

The Thin Positive wire from the battery is very important. This thin wire is what runs everything in the car and charges the battery. If this wire, often a fusible link, is bad then the car is going nowhere.

Testing

You cannot test big wire with common Ohm meter. Most meters uses a tiny battery and can't test much beyond 18 ga. Use a Voltage Drop test instead...

Need a good meter & probes, get very good connection at ends of cable, start the engine while watching volt meter. >0.2v? Cable is bad or you didn't do test right, likely crappy probes or probe connection at end(s) is suspect. (If meter show -v, ignore it... means you got probes backward.)

If engine start easy and you can't read meter, disable ignition by pulling power at module.

GM & AC Delco replacement battery cables

These cables are well made using parts from Delphi Automotive. They are very good cables but there are a few things to keep in mind. (You can't over protect battery cables in this car...)

The battery end of these cable assemblies is barbed to displace lead on the battery terminal. This prevents rotation that can loosen the bolt and I expect they also get a better connection than simple flat terminals. It is important that these cable ends not be disturbed anymore than absolutely needed.

When possible, you are better off to disconnect the block/body ends of the cable when you need to work on other electrical components. This will avoid needlessly tearing up the battery terminal face. Shove the free end(s) into a pill bottle and tape it in place.

Before you install a new one of these cables, pop out the bolt, pull off the cover, and coat the crimp with dielectric grease to seal out moisture. You can also do this to the other end if you push the rubber sleeve up the wire.

When you install these cables on the battery, aim the cable down some so that any water that gets into the cover can drain.

All AC Delco cables are made as "positive" leads but they all come in black. Go Figure... This means they all have a fuse link with a length of wire on them. They give you plenty of wire to work with and it is ok to trim the wire and/or put a different terminal on the end if needed. Don't alter or damage the fuse link. (Having a fuse link in the thin ground wire isn't ideal but it won't hurt anything.)

C500

C500 is the large bolt-together terminal block by the battery. (It's on the firewall for 84.) If you take this apart for any reason, check it over very carefully. If needed, clean and grease it with dielectric compound. Some of the wires in this block carry hefty currents. Dirty terminals in here can produce some bizarre problems. Items like the tachometer feed, coolant fan control, ignition power and the starter solenoid circuits run through here. (Exactly what runs through here depends on model engine and year of the car.)

If you have to clean out the block, don't use solvents that will eat plastic. If you can't get contact cleaner from Radio Shack or some other electronic supply shop, try brake parts cleaner or EFI cleaner. These should be more plastics friendly than carburetor cleaner. Test them on a spot where they can't do any real harm to make sure. Blow the block dry with compressed air before you pack it with dielectric. (Use a "canned" air product if need be.)

Note: ECM signals do not run through C500. Sensors and ignition control lines are wired directly to the ECM through one or two bulkhead seals on the firewall.

Power Distribution block

Note: 84 does not have a Distribution block. See link size and location in the ugly details on fuse links.

The main terminal block is below C500 in most Fiero. With one exception this block caries the power for the entire car. The only thing not drawing power from this block is the starter motor.

In my 87SC, the terminal block has a large stud and a small one.

The alternator and ECM feed are crimped to a large lug that spans both terminals. Whenever working on the terminal block, this lug will be the last one removed and the first one installed.
The large terminal is where the feed from the battery should go.
The small one has two fuse links attached that feed everything else in the car.

It is extremely important that all connections to the terminal block are clean and solid. This terminal block should be one of the first things checked when you have electrical problems. There is allot of current flowing thru here and any corrosion will cause voltage drops that can cripple the whole car. (How much current? The entire output of the alternator flows thru here. That can be 100 amps or more.)

Here's a map of the main terminal wiring.

Grounds

GM usually runs three main grounds. All must be in good shape to prevent problems.

Battery to Block. Direct run with heavy cable. Main purpose is to provide return path for starting current.
Battery to Body. Direct run with light wire. Secondary return path for body/chassis to battery and alternator.
Body to Block, 2 times. Primary return path for body/chassis to battery and alternator.
Head bolt to frame with bare braided conductor. Provides return path for most of the car. The braided wire carries more current than regular wire. If you replace these, use another braided strap.
12 gage wire from trans bell housing bolt to frame. This can rot from road salt etc.

These small grounds will cause major problems:

What	Where	Why
G201	Behind Radio, Hidden by Radio's rear brace.	These grounds are use by most interior items and Fuel Pump.
G202	Between Seat, Below ECM
G301	Under Dash on passenger side A piller	This is used by Power Windows and Power Mirrors.
G101	On LF Fender, Below Headlights	Grounds for: All front lights, Radiator Fan, HL Motors & Relay/Module.
G102	On RF Fender, Below Headlights

G101 & G102:
G101 may have two end screwed to the frame. Small wire runs most. Big wire runs radiator fan. Fan problem then check G101 too.
G102 is a redundant thin wire.

G201:
Service manual, Alldata, and some others are wrong for 87-88 cars. They say "Splice S201: Main Harness, Above Steering Column" but it looks like a typo. The location in table above is correct.
You can inspect G201 without removing the radio. Look Behind the radio's vinyl shroud on driver side.

Pontiac seems to have been in the habit of attaching the braded body to block ground strap to the stud for the deck lid hinge. This isn't the best place for it. The hinge adds more layers of paint etc. Find a spot to anchor it to the side of the bracket the hinge is bolted to. You may need to drill a hole and/or get a longer strap. Make sure the new bolt doesn't interfere with anything important.

They also anchored the thin ground from the battery to the battery tray where it's hard to inspect. I moved mine to the frame lip right next to the battery. Now I can easily inspect it any time the vent grate is off.

On the 4 cylinders, I don't remember what they did on V6, GM used a stud topped head bolt for the heavy battery grounds. It's a common problem for that anchor to corrode heavily. If that happens don't try to force it or you could rotate the head bolt. Cut the nut off the stud. It doesn't matter much where you anchor the ground to the head or block as long as it's clean and won't stress the cables when the engine moves. (Stay off the water pump!)

Many people are familiar with the main grounds but there are also a bunch of ground wires for the ECM and ignition bolted to the block and transmission bell housing. These must all be clean and tight. You can get all sorts of weird errors if these are crappy. Any time you get Ignition or O2 sensor errors you should check these grounds before doing anything else.

Cleaning

When you clean the wire ends, don't forget to clean whatever hardware and frame holds them. Get everything to bare metal, including removing any paint.

Coat the terminals and hardware with grease or better yet dielectric compound. All you want is a very thin film of grease. In some cases, too much might interfere with getting good connections.

With bolt/screw terminals, snug the hardware just enough to put pressure on the lugs. Wiggle the lugs against each other a bit to make sure they get good metal-to-metal contact. Be careful and don't pull on the wires or bend the lugs. Tighten the nuts the rest of the way then coat everything with dielectric grease to help it repel water.

This will keep them from corroding far longer than simply cleaning them. Dielectric compound is Silicone based and resists washout by chemicals like engine cleaner or car washes. Don't forget the battery and other terminals are directly exposed to weather and car washes. Oil and grease is pretty easy to wash away under these conditions.

There are numerous commercial products to stop corrosion on the battery terminals. Some work better than others. I find it just as easy to use dielectric compound on them. This saves buying yet another chemical and works as well or better than any of the commercial products out there.

Using Grease/Oil

Simple... Don't. Grease and oil can kill plastic, some fast and some over time. Worse, some grease and oil contain metal and other material that will create a short circuit or a "Soft" Short. Soft short is short with resistances that won't blow a fuse but it cause a problem all the same.

Dielectric Grease or Light Bulb Grease will be safe. (Bulb Grease will not run in hot systems.)

Splicing

Before you install a crimp terminal, work some dielectric into the wire strands to seal them. Do this if you use those bolt-together repair ends for the battery cables. This will keep the wire from drawing water up under the insulation. On battery ends, it will keep acid out as well.

All splices in sensor wires should be soldered and sealed with weatherproof shrink tubing. Even small amounts of corrosion in these wires can screw up signals to the ECM.

If you can't solder:

Clean the wire. Including the insulation! The weatherproof shrink tube likes clean surface.
Pack the wire with dielectric compound. (It keeps any moisture that gets in from eating the joint.)
Slide some weatherproof shrink tube over one of the wires.
Install a non-insulated crimp sleeve.
Shrink the tubing over the joint.

If you can't get weatherproof shrink tube, coat the joint with dielectric compound and cover it with regular shrink tube.

Do not use standard electrical tape except for emergency repairs. All emergency repairs must be redone as soon as possible or you'll have trouble down the road.

Posi-Lock connectors are good for emergency or permanent repair of most wire in the car. For sensor leads, I still recommend a soldered joint but these will work much better than simple insulated crimp terminals.

This Metric to AWG wire chart may be handy for some people. It lists common metric sizes and the correct AWG wire to use with it.

Weather Pack connectors

There are several types of weather resistant connectors used by GM. All of these connectors have silicone seals where the wire enters the shell and between the shell halves. Under normal conditions, no other sealant or dielectric is needed.

On connectors in low places, I still pack them with some dielectric compound. The connectors on the 4 cylinder distributor or DIS brick are good candidates for this. These connections are low enough to be hammered by deep puddles.

Connector Repair

Weather Pack connectors are used for O2, MAP and other things on all Fiero models. The shells on these connectors can be replaced without cutting the wire. You'll need a terminal tool like Lysle # 14900 or MotorMite # 85360. You can reuse good salvage shells or find new ones thru auto supply shops. (See links at end of page for other sources.)

Open the back of the shell (Pry up the locking ears on the side of the shell to open the cover.)
Insert the release tool into the open end of the shell until it bottoms out. (The release tool slides down the outside of the terminal to squeeze the locking ears.)
Pull the wire and terminal out the back of the shell.
Insert the wire into the same position on the new shell.
After all wires are transferred, close the back cover on the new shell.

Expanded view of Weather Pack connectors.

Metri-Pack

Metri-Pack "Pull to Seat" connectors are used for sensors starting with the 1987 models. "Pull to Seat" connectors are generally smaller than Weather Pack connectors and they cannot be fixed without cutting the wire. If one of these connectors is damaged, it will be easier for most people to obtain new prewired connectors from a parts store or good used ones from a salvage yard and splice it to the harness. (These "new" connectors are used for IAC TPS MAT and ECT in the 87-88 Fiero 4 cylinders.)

Why do they call it "Pull to Seat?"

See This

If you are having trouble identifying a connector type, visit Motec's site. Most of the ones in Fiero will be in the Weather Pack or the MetriPak P2S pages. If the one you want isn't shown, this will at least give you an idea which family it belongs to.

Yes, you can get loose parts for Pull to Seat connectors if you really want them. No, I'm not going to explain how to work with them in this article.

Packard

Packard, often marked "PED" (PED = Packard Electric Division), is used on inside wiring. Back-loading terminals can be removing with small wire, IE paperclip, or very small screwdriver. Too many styles to list here and each one need a different method to remove them.