'76 electrical issue(s)

dingo · Post by **dingo** » Fri Apr 22, 2011 8:44 am

sounds like you have it right.

http://www.vintagebus.com/wiring/bus-76.jpg

click to enlarge

bottom left: C is alt. C1 is VReg T1a is connector you are looking for (ignore J14 heater blower)

dtrumbo · Post by **dtrumbo** » Fri Apr 22, 2011 9:23 am

Below are some excerpts from the wiring diagram for an otherwise stock '76 bus. Hopefully yours hasn't been molested to the point these become irrelevant. If not, I think this will clear stuff up for you.

poptop tom wrote:What is the red wire being mentioned?

The red wire is connected with the blue wire at the connector that plugs onto the voltage regulator (designation C1 in the diagram). While we're here, you can see what Colin is talking about regarding the split that goes to the heater blower fan (designation T in the diagram).

poptop tom wrote:I have a blue wire hanging 5" down loosely from the plug that goes into the VR. I have no blue wire sticking up out of the harness where I assume I should.

Are you saying the blue wire hanging 5" down is not connected to anything? If so, that's one of your problems. That blue wire should go all the way to the front of the bus and attach to your dash warning light. Here's the big picture.

... and another smaller excerpt that shows the dash light (designation K2).

poptop tom wrote:I have a blue wire behind the dash that goes to the bulb of the alt light. Where this wire goes I have no clue.
I assumed that it ran directly from the alt light to where it needs to be hooked together with the blue wire coming out of the VR.
Which is why I ran a wire direct from the alt light to the VR as a test. Is that wrong?

You are correct as evidenced by the above diagrams. From what I've read, I think you have a couple of issues. One, your alternator has an issue (shorted diode(s)?) and your warning light isn't connected to your voltage regulator which is necessary for a healthy alternator to do what it do (the blue wire provides the excitation voltage).

If it were me, I'd get the alternator to a known-good condition and then restore your wiring and I'll bet everything works as it should.

dtrumbo · Post by **dtrumbo** » Fri Apr 22, 2011 9:24 am

Yeah, what Dingo said.

poptop tom · Post by **poptop tom** » Fri Apr 22, 2011 9:36 am

Dick and dingo - thank you both. Colin as well.

Yes Dick, you have described it perfectly. And I ran a "new" wire from the alt light behind the dash and tied into that blue wire
at the VR. And I still have a draw on the system. (thats why I was wondering where the blue wire came up out of the wiring harness).

I will reluctantly pull that alt and get it back to the guy that did the previous work, and have him check out/replace those diodes!

FYI - I have tried three different VR's as part of my "troubleshooting".

poptop tom · Post by **poptop tom** » Tue May 03, 2011 1:09 pm

So I got the alternator pulled, and dropped off to the rebuilder. Hopefully it's the diodes, and he can locate replacements.

What a pain in the ass it is to pull the 70 amp alternator!

I followed ratwell's detailed description for pulling it. I couldn't get it out of there for the life of me. I ended up removing the bottom nuts off the moustache bar and using a bottle jack to jack the engine just a tad. In doing so, I realized I could now loosen the oil fill tube (which I suspect was a source of a light oil leak anyway). I removed one nut, and was able to turn the fill tube to the drivers side, just enough to squeeze the alternator out of that small opening!
Holy Toledo. I hope it gets repaired and I dont have to deal with removing it again.

Post by **Amskeptic** » Tue May 03, 2011 2:10 pm

poptop tom wrote:So I got the alternator pulled, and dropped off to the rebuilder. Hopefully it's the diodes, and he can locate replacements.

What a pain in the ass it is to pull the 70 amp alternator!
I followed ratwell's detailed description for pulling it. I couldn't get it out of there for the life of me. I ended up removing the bottom nuts off the moustache bar and using a bottle jack to jack the engine just a tad. In doing so, I realized I could now loosen the oil fill tube (which I suspect was a source of a light oil leak anyway). I removed one nut, and was able to turn the fill tube to the drivers side, just enough to squeeze the alternator out of that small opening!
Holy Toledo. I hope it gets repaired and I dont have to deal with removing it again.

I don't remember ever having any difficulty removing alternators. Right rear and center rear tin. Belt. Cover plate with that 10mm bolt and alternator pivot bolt both removed. Belt adjustment/heat exchanger bracket. Wire from starter + VR plug harness out of right upper cylinder cover. Loosen upper cylinder cover screws so you can pull up just enough to get rightside fresh air pipe (10mm bolt holding it to exchanger) out from the cover and exchanger. Plastic portion of oil fill pipe. Pull right to clear pivot bolt bracket then towards rear bumper and up at a twist to clear fill pipe?
Colin

poptop tom · Post by **poptop tom** » Tue May 03, 2011 5:38 pm

Yeah I had hoped it would work that way. But it wasn't! I'm just glad its out. Next I need to pull the starter and take the solenoid apart to clean and lube it. Hopefully that will solve the issue of it not engaging on the first turn of the key.

poptop tom · Post by **poptop tom** » Wed May 18, 2011 8:15 am

Update - Nothing too new to report other than I pulled my alternator and took it to the shop that originally rebuilt it last summer.
Popped by there a couple of days ago. He pulled it back apart and rechecked everything. Diodes were supposedly good. He put it back together and says it now has no output.? Huh? He says it could have an issue with the windings (or something like that).
If the 70 amp. alt. is not repairable, I'll be pissed. Sourcing another will be difficult. They are tough to find, and expensive when you do find them. Not to mention, I already have everything for the 70 amp - cooling boot, harness, adj. bracket, etc.

I also pulled my starter and ordered a new solenoid.

Post by **Amskeptic** » Wed May 18, 2011 9:32 am

poptop tom wrote:Update - Nothing too new to report other than I pulled my alternator and took it to the shop that originally rebuilt it last summer.
Popped by there a couple of days ago. He pulled it back apart and rechecked everything. Diodes were supposedly good. He put it back together and says it now has no output.? Huh? He says it could have an issue with the windings (or something like that).
If the 70 amp. alt. is not repairable, I'll be pissed. Sourcing another will be difficult. They are tough to find, and expensive when you do find them. Not to mention, I already have everything for the 70 amp - cooling boot, harness, adj. bracket, etc.

I also pulled my starter and ordered a new solenoid.

Second opinion time?
Colin

poptop tom · Post by **poptop tom** » Wed May 18, 2011 1:02 pm

That's what I'm thinking Colin, but I just dont whom locally is the person(s) to go to.

All of this is pissing me off and taking a toll on my patience. So yes, probably time.
Especially when I have a beautifully built engine waiting to get itself back out on the road.

poptop tom · Post by **poptop tom** » Tue May 24, 2011 5:19 am

Well my alternator rebuild guy says the diode pack (he called it the resistor pack) is bad and needs replaced.
These are NLA parts apparently so he is looking through his huge catalog of alternator parts to find a similar, suitable replacement that he can retrofit into the alt. He says I may even end up with a bit of additional amp output - maybe up to a 90 amp.
If this works out, will the additional voltage have any effect on the VR?

Also, I located a company that has a rebuilt 70 amp for $269. One through BD is $322. I have left a message at a place called Precision Parts. Ratwell lists them as a potential source.

Any thoughts on all of this?

EDIT - I also found this.http://parts-catalog.acdelco.com/catalo ... search.php

Sold by this company.http://www.rockauto.com/

Post by **Amskeptic** » Tue May 24, 2011 3:48 pm

poptop tom wrote:Well my alternator rebuild guy says the diode pack (he called it the resistor pack) is bad and needs replaced.
These are NLA parts apparently so he is looking through his huge catalog of alternator parts to find a similar, suitable replacement that he can retrofit into the alt. He says I may even end up with a bit of additional amp output - maybe up to a 90 amp.
If this works out, will the additional voltage have any effect on the VR?

Amperage does not increase voltage.
Colin

poptop tom · Post by **poptop tom** » Tue May 31, 2011 10:27 am

Woohoo!
No more alternator light continually on or draw on the electrical system! Rebuilt alternator was what it took! Red light comes on, and then goes out as it should!
And it charges, too!

Time to finish cleaning it up, give her a bath, take it for a spin, and a fresh tank of gas!

Heck, I may let Belleplaine go for a ride if the weather doesn't get nasty. He's suppose to be in town on a sales call!

I'll get into some of details of the reman. alternator I purchased at another time.

Itinerant Air-Cooled

Itinerant Air-Cooled

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