Dead fuses and power taps in 1989 Convertible fuse block (SOLVED with new photos)

[JensenHealey]

I have posted here before about some issues my 1989 Convertible has with various electrical subsystems that do not work. Briefly the list is:

Things that work:

• starter
• gauges
• hazard lights & turnsignals
• brake lights
• power windows
• power top motor (I can hear when working the switch but I don't know if it actually raises or lowers the top)
   

Things that don't work

• headlights
• taillights
• reverse lights
• gauge lights
• trunk release
• gas lid release
• power seats
• fuel pump

I have continued investigating this and I have discovered that there are two fuses that seem to have no power supplied to them when the ignition key is turned to the ON position. Also there are some BAT power taps that I believe are supposed to be supplied power all the time and these also do not have any power available at any time irrespective of the position of the ignition key.

The dead fuse positions are TAIL LP and CTSV-CLK. The Dead power taps are two near the bottom of the fuse box with a label of BAT and another in the upper half of the fuse box labeled LPS or maybe LP5. Can anyone tell me what the LPS or LP5 or BAT power taps are? Also what is the fuse at the very top of the box with the label of C/H ? Am I correct that these BAT power taps should have power continuously? 

The lower BAT power tap has a red wire and a blue wire going into it. The upper BAT power tap has an orange wire in it. The LPS/LP5 power tap has a grey wire going into it. These can be seen in the lower photo.

These are shown in the image below (arrows added to fuse box diagram posted by IndyJim):

Edited February 17, 2021 by JensenHealey
added fuse box photo

[IndyJimW]

The wiring diagram that I posted shows Power Distribution on pages 2-4. There are 3 fusible links on the starter supplying power to the ignition switch and fuse block. Check for blown links or corroded wires at the plug going thru the firewall. If it is like my Avanti the problem is before the fuse block not from the fuse block.

Good luck,

Jim Wood

[JensenHealey]

Thanks Jim

Which specific plug through the firewall are you talking about?

I do see what I think is a large bundle of wires in a "plug" like structure going to the firewall but I have not figured out how to "unplug" anything there to examine the inner workings of any connection.

[IndyJimW]

The firewall plug usually has a captured bolt in the center of the outside plug that clamps the plug halves together. The outside of the plug should be clipped to the body. The inside part of the plug should release when you loosen the bolt. My firewall plug is located between the wiper motor and the washer tank.

Good luck,

Jim Wood

[JensenHealey]

Based on suggestions from IndyJIm and looking at the power distribution wiring diagram he uploaded recently I have come to the conclusion shown below based on the list of dead circuits I have in my 1989 convertible

[IndyJimW]

The fusible link in basically a piece of wire that is a smaller gauge then the regular wire, so it melts first. You should see a burnt spot in the wire in the first six inches coming off of the starter solenoid. You can grab and pull the wire and it will separate at the blown area of wire.

Good luck,

Jim Wood

[JensenHealey]

Does a fusible link have a particular rating like a regular fuse or circuit break that determines under what load it will melt?

[IndyJimW]

Yes, it should be marked on the wire coating.

New links are available from most auto parts stores, but since you have to wire it in, I usually just wire in a fuse holder.

Good luck,

Jim Wood

Edited February 18, 2021 by IndyJimW

[JensenHealey]

Yeah, replacing with a real fuse seems like the way to go. Do you think a 30 amp fuse would be appropriate for that location?

Edited February 18, 2021 by JensenHealey

[IndyJimW]

Is the fuse bad?

It is a 16 gauge fusible link, you can get them at any auto parts store.

https://shop.advanceautoparts.com/p/dorman-conduct-tite-16-gauge-gm-fusible-link-wire-carded-85621/22141316-p?c3ch=PLA&c3nid=22141316-P&adtype=&product_channel=Online&store_code=&gclid=c46e972d0f731595731bf703cfcc9449&gclsrc=3p.ds&msclkid=c46e972d0f731595731bf703cfcc9449&utm_source=bing&utm_medium=cpc&utm_campaign=b_lia_all_dorman%2Fretail%2Fbody_electrical_terminals%2Fconnectors_review_all_rmktg_aap_us_all&utm_term=4581183924589470&utm_content=Bing_LIA_Dorman Retail %2F Body_Electrical_Terminals %26 Connectors_Review

If you use a fuse I would start with a 20 amp MAXI fuse.

Good luck,

Jim Wood

[JensenHealey]

This evening I finally went over to my shop to investigate this further. I ended up unbolting the starter from the engine block so I could completely disconnect the whole wiring harness from the starter. After doing that and disconnecting a single wire going to a sender (oil pressure perhaps) on the side of the block near the starter, I was able to pull that complete section of the wiring harness up from below the engine to the top of the engine compartment so I could examine it and work on it much easier. I found that there were three 16 gauge fusible links and one 12 gauge fusible link connected to the power post on the starter solenoid. I found a spot on the 12 gauge fusible link that was heavily corroded. I didn't have time to completely confirm this is the issue or even take a photo of the damage. I will do that tomorrow.

[JensenHealey]

I spent another couple hours working on the dead circuits issue on the 1989 convertible this evening.

Here are some photos showing what I found when I pulled the wiring harness away from the starter solenoid.

Other than the main positive battery cable these are all of the wires that are normally connected to the positive supply lug on the starter solenoid.

These are two photos of the main positive battery cable that was connected to the positive input on the starter solenoid. The green corrosion on the cable lug and the rust on the starter terminals do not look very good at all but this turns out to not really be the root cause behind the dead circuits for headlights, taillights, and etc.

This blurry photo is a closeup of the main positive connection from the starter solenoid to the positive post on the alternator. Even though the photo is blurry, I hope the greenish corrosion can be seen. This too is bad but yet again this is not the primary cause of the dead circuits.

These two molded connectors that make the transition from the fusible links to the regular wiring are the REAL cause of the dead circuits. These molded connectors do not pass any power through them. As a temporary fix to confirm this is the problem I cut these out of the harness ends and replaced them with standard crimped butt connectors to connect the fusible links to the regular wires in the harness and then hooked them all directly up to the positive post on the battery and HEADLIGHTS ARE NOW WORKING!!!

Yahoo!!!

Next I have to figure out how I want to make a permanent fix.

[studegary]

Maybe I am incorrect, but I am thinking that what you show is the fuse part (that is bad) and by eliminating it you are simply taking the fuse out of the circuit (not good).  I am sure that someone will chime in and correct me if I am not thinking correctly this morning.

[JensenHealey]

No, the small diameter piece of wire is actually supposed to burn through.

See the following article on fusible links: https://itstillruns.com/causes-fusible-blow-car-12161001.html

When it fails it should look something like this:

[IndyJimW]

That’s where it blows, replace with new fuse.

Good luck,

Jim Wood

[studegary]

15 hours ago, IndyJimW said:

That’s where it blows, replace with new fuse.

Good luck,

Jim Wood

Thank you.

[IndyJimW]

JensenHealey;

Sorry , I get in mechanic mode and don't explain what I'm looking at well.

GM used fusible links to protect the main wires supplying multiple devices. Today everyone uses MAXI fuses. These type of fuse are slow to blow, unlike the fuses in the fuse block. Fusible links rarely blow, I've only replaced a handful in 45 years.

Yours is blown, you can tell it was hot because the red end is pinkish in color. This can happen one of two ways. Corrosion got to the wires, broke enough wire strands and the fuse overheated. OR too much current melted the outer wire casing and corrosion set in.

I install a fuse to test the system because these are a pain to replace.

Use a amp meter to test the system as you power on all the devices powered by the wire.

You can also wire it direct and follow the melted wiring to the problem, not a method I'm fond of 😫.

Good luck,

Jim Wood

PS - Did you get your fuel pump running?

 

[JensenHealey]

9 hours ago, IndyJimW said:

JensenHealey;

PS - Did you get your fuel pump running?

 

I pulled the fuel tank this evening. Once it was on the ground, I decided I had enough for the day and came home to make pizza.