I saw that 138milkmen had a similar issue but did not want to hijack his thread. I've had the car out twice this summer (just got it legal first time in 12 years) It is a 72 cutlass convertible 4spd with a 68 455 F block with C heads. Last Friday I drove it for about 30 minutes around town and it ran great (well good) - on Memorial Day I drove 5 miles to the store (highway speed) and half way back suffered total electrical failure - no lights nothing - I towed it home and discovered that when I got the car running last summer I wired the positive cable down through the tube at the back of the block - the returning red wire that goes to the horn relay was tight against the block and melted in half - i learned from your replies that that is suppose to be a fusible link (first I ever heard of one) and that the block needs to ground to the fire wall (strap is on block - I just never connected it) I put another red wire to horn relay (is that the junction box? Aka J/B on wiring diagram?) after putting new wire in I am still 100% dead - battery tests good - positive wire tests good - no power at horn relay - please help - I am pretty new to this but bought a good multimeter and test light - I am about 25% junk yard / 75% YouTube mechanic but learning more and more all the time so appreciate any help and your patience - thanks all! ~ Joe

 

There should be a fusible link at the "JB" junction block attached to the horn relay for the red wire that runs from there to the bulkhead connector. It feeds everything in the car including headlights. You can verify the lack of power by checking the fuse for the tail lights in the fuse block with a meter.

 

The bolt with all the wires going to it the junction block? And what's the bulkhead connector?

 

Yes that's the junction block. The bulkhead connector is under the brake power booster. By your picture it looks like someone replaced one of the heavy red wires.

 

Yes, that's the junction block on the horn relay.

Take all of the wires off and heck to see whether you have power at the thick wire from the battery.
If not, then the problem is in that wire somewhere.

The bulkhead connector is the double-plug that goes through the firewall to the fuse block.

- Eric

edit: Beat me to it.

 

thank you. Yes I replaced the red wire - old one burnt in half on the block. I'm not at the car but will check it out.

 

So thats the wire back to the starter. I don't see a fusible link there either, looks like the wire on top had the terminal changed.

 

thanks for the tip! I will disconnect the wires and try just the thick one when I get to the car.

 

should I add a fusible link to the starter wire? And if so can I do it on the end coming from junction block?

Not it sure what that top wire is yet (will check it out)

anyone have ave any good suggestions (detailed) on routing the starter wires in 72 4spd with 455? It's aweful tight down there - between block - exhaust manifold - and the clutch linkage

 

Do you have a CSM? It shows the correct routing for the 4spd.

 

That chasis service manual?

 

Yes sir.

 

i will order one right now - any recommendations between cd-rom vs. paper?

 

OPGI doesn't seem to have a 72 wiring diagram - know where I can find one?

 

An original CSM can usually be had on Ebay.

 

Thank you for all your help today (and for the hope - was feeling pretty defeated) i will try everything on my end as soon as I am able and post results. Have a great weekend.

 

Let us know, it should not be hard to figure out.

 

Update - I took the red wire from starter to junction box and read it that way and this is what I came up with (battery reads 12.76) should this read the same?

 

You said all the power is dead? Let's start with the basics. With a DC voltage tester (analog or digital), after you've tested the battery, put one lead on the horn relay and the other on the negative side of the battery. Look for the meter to show the voltage you started with. If this checks out, go from the positive side of the terminal to the engine. You need to start at the source of power to make sure your battery cables are good. I've recently had an intermittent connection on the negative cable which will cause discoloring on the starter terminal and prematurely burn the solenoid. It will also cause the problem you are experiencing. Check the negative connection at the bottom of the left head as well. Once you have determined those are good move down the line going from positive to negative or negative to positive. Doesn't matter which you start with just make sure you criss cross all the way through. Once the negative cable hits your engine block it travels through the rear grounding strap from the right head to the firewall. This is what makes the rest of the chassis the negative. At this point the negative is checked. Follow your wires and the diagram and continue through until all the positive wires are checked. Nuts, bolts brackets will do the same but the only sure connections are ones designed for this purpose (wires or braided straps). I'm willing to bet your issue is a bad negative connection.

If this all checks out in the engine compartment pull the harness/ junction box to the firewall and check for corrosion. If that checks out start your analysis in the car. Check to see if the rod is hitting the harness at the bottom half of the steering column correctly. This would have nothing to do with the lights and horn but I've seen this be the cause of a car not starting more than once.

Chasing an electrical issue in general takes patience. In a 45 year old cars it takes lots of patience. Refrain from the temptation of short cuts it will only frustrate you. If you are getting frustrated walk away and come back when you calm down.

OK I now see you have a digital meter. Start with the basics first. Then work your way from the battery to the junction box.

 

What do you read at the junction block?

 

From positive battery to ground on block - same reading from head through chain to firewall

 

This is the reading from negative on battery to the end of the red wire that goes to starter (disconnected from horn relay to single out wire) - when I connect it to horn relay (junction block) it reads 0.0 - is it suppose to always read 12.75 no matter where I check it? (yes I'm that new)

 

There should be 4 red wires at the junction block?
1 runs between the starter and the junction block.
1 runs to the voltage regulator from the junction block
1 runs from alternator to the junction block
1 runs from the junction block to the bulkhead connector on the firewall. This wire has a fusible link at the junction block.

 

there is - I disconnected all the wires and read the end of the one that goes to the starter - it reads 0.32 is that what it should read?

 

It should read the same as the battery if the big battery cable goes to the starter first.

 

if the end of positive cable is good - and end of that red wire is bad - does that mean it's the starter? Doesn't seem like the starter would kill the headlights and all?

 

Do you read 12+ volts at the starter? Is there a fusible link on the wire from the starter to the horn relay junction block at the starter end?

No the starter isn't determined bad at this point.

 

Yes 12 at starter - no fusible link on the wire (I replaced it after the old one burnt in half on the block - I will add a fusible link to this wire or is an actual fuse fine? And can I put it on the end that goes to horn relay or does it halve to be down at starter? Would this make a difference at this point that this wire isn't reading 12v?

 

Don't get ahead of yourself yet... You have a bad terminal lug connection on either end of the wire or its broken somewhere in between. Can determine the issue by looking at the wire?

 

it's new - I crimped the ends on both ends - I'm going to pull the starter and double check positive end at starter because I'm doubting myself - get back to ya - thanks for the help by the way!

 

If you have 12v at the starter and the only connection to the junction block from the battery is that wire, then you have a bad connection in one of your crimped terminals. There is no need to pull the starter just redo the wire. That wire is supposed to be connected to the same place as the battery cable.

 

The only fusible link according to the wiring diagram is the wire that runs to the firewall.

 

thanks - yeah have to pull it to get to it though - very tight in there - is there a way to test just bare wire once I have it out? Should I test starter to see if I fried internal wires in it or something?

 

Woot!!!! She's up and running!!! It was a bad wire from starter to junction box - (seems I have to do everything twice - same thing happened with Napa selling me a bad fuel pump hehe) thank you all so much! I know it seems like an easy deal to you all but I sure was stressing it hehe. I did learn a lot from you guys though - thanks again!

 

Your quite welcome, glad you got it up and running. That's what is cool about this hobby, the personal satisfaction of accomplishment.

 

Glad to hear you got it fixed, and thank you for troubling to tell us what was the problem and how you fixed it. Too many times we never know how or if someone dealt with a problem.
You won't find better help for anything Oldsmobile related than here.

Roger.

 

Agreed! You guys are All amazing!

 

The first harness I always replace is the engine harness.

It takes the most heat and abuse.

Cheap insurance.

 

I think I will follow your example - but having too much fun driving it at the moment - I think I will do that this fall - thanks!

 

If the wiring is good, not frayed or brittle then your harness is fine and there is no reason to change it. Drive and enjoy.