I'm having a problem getting 12 volts to my Heater system input on my 78. I have temporarily rigged up 12v to the heater system and it works fine when I can get power to it.

I have checked and replaced all the fuses that were blown or that just looked dodgy. When I put a volt meter on the Heater A/C fuse I get varied readings (+ 0.5 volts, the occassional -0.00 volt), this is the case with the engine running too. I have checked the entire fuse block and I get 12 volts on every fuse except the top right 3 fuses (looking directly at the fuse block). The other two may be a result of the same thing that is causing my heater voltage supply problem.

I have tried to remove the fuse block, I could find only 2 bolts. Looking at a repair manual there are only 2. I cant get the damn thing to budge.

I noticed that in the engine bay there are a whole pile of wires going into/coming out of what looks to be at the same position as the fuse block on the inside of the firewall, are these connected??? The manual I have here shows that it could be separate. It only shows a brand new wiring loom.

Anyone had a similar problem? Any general advice on common problems? Will that fuse block just come out easy??

I think from memory, the top right fuse is the heater/AC, then Dir Sig / Backup and then Gauges 3rd from the top, I think. These dont show 12v at all.

Cheers

 

 

 

 

 

 

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Kiwi Doug

aka Harry Tasker

I would check your fuse links located where the wires go into the fusebox from the engine side. There are at least 2 of them.

If you look closely at the center of the wire harness, engine side, where it goes to the fuse box(...a whole pile of wires going into/coming out of ...), you'll see a small bolt in the middle. Take this bolt loose(it will NOT come all the way out), and you can separate the fuse box from the main harness.

I agree with Big Fish on checking the fuse links first, tho. They should have 12v on both sides of the "links". There are several on the car, in various places. A wiring diagram should show them, and their locations.

Are you checking for voltage with the key on, or off? It will make a difference, on some circuits.


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Joel Adams
C3VR Lifetime Member #56    
My Link


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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Thanks for the tips, particularly for the tip about the bolt on the engine side, that sounds like it will make all the difference. On the engine side of the fuse box it's a bit dirty so it was hard to see anything.

I have been checking voltages on both ends of the fuse, with the key on and off just to make sure. Do the wires on the engine side individually unplug (or in groups) or ar ethey just one big connection?

I almost had the interior fully put back together on Saturday and ready to drive her again but this problem had me going in circles, maybe next weekend now.

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Kiwi Doug

aka Harry Tasker

The con. block(bulkhead connector) on the eng. side is normally split into 2 sections, but I'm not sure on the '78. All of the terminals can be removed individualy, after separating the connector, but it is basically one big connector.
I solved a problem similar to this on my '85, by unbolting this "bulkhead" connector, and cleaning all of the terminals. I suspect you will have the same luck!
Adams' Apple38696.9109027778

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Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Thanks again, that'll be my first job next weekend.  I am hanging out to drive her again, all this nice weather down here is going to waste.

Cheers

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Kiwi Doug

aka Harry Tasker

Well, I pulled it al apart, again and again, after cleaning the terminals and testing etc but I still cant get 12 volt on the top right two fuses

Behind the two fuses there is a big orange wire going to them, common 12v I'm guessing. Ignition on or off it wont power up.

I jumpered 12v from another source to the same connection as the orange wire and the heater fan etc powers up which is what I need it to do. The other item requiring power from that same orange wire on the fuse box is the turn signal, that doesn seem to work even if I jumper 12v to it, so that's another problem, yippee.

The orange wire that is meant to deliver 12v to the top right two fuse disappears up the wiring loom. I've cut back a little insulation tape to see if it comes back down but it seems to keep going up to somwhere else.

I have 4 books here about 68-82 Vettes but none go deep enough into detail about the wiring.

Does anyone have any more detailed wiring diagrams for a 78 or does anyone know where the orange wire goes? I'll try to fix the direction indicator proble later once I can get power to it, the yway it is meant to.

I dont really want to have to pull my dashboard back out if I can help it.

 

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Kiwi Doug

aka Harry Tasker

Doug, it sounds like you have a blown fuse-link.
If you can get under the car, check around the starter for 2-3 red wires, comming off of the center terminal of the solenoid. (The really big one is the batt. cable)

About 4"-6" from the solenoid terminal, you will see what looks like small "tootsie-rolls"(I guess you guys have them down there!). These are fuse-links. One or more of yours is burnt, simmilar to a blown fuse, but you can't just look at it and tell it's blown.

With the batt. connected, test for 12v on both sides of the fuse-link(s). If you look hard enough, you'll see that at least one of these red wires turns orange after the fuse-link. When you find the blown link(s), jumper around them, or cut them out, and splice the ends of the red/orange wires back together, just as a TEST. If you now have power at the fuse box, then you have found the problem. You do NOT want to leave these wires spliced like this- you must have some form of circuit protection.

There are auto parts stores that stock these links, but I don't know about your location. If you can't locate fuse links locally, I know some of the dealers used to have them, and some of the 'Vette vendors carry them.

Hope this gets you on the right track!

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Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Adam's has it right about the MAIN fuse link located at the starter, but I don't believe that's the one you need because you have partial power. At the bulkhead connector on the engine side there are 2 (orange 20 gauge) fuse links. Most likely it's one of those that opened. Check for power on BOTH ends of the links. Any auto parts store should carry replacement links with crimp connectors. There is also a 16 gauge red link, but that supplys the entire fuse block. Try these people for a laminated wiring diagram for your car: http://www.lectriclimited.com/

Note: on the factory diagrams fuse links are referred to as "thermo wire"

Big Fish38696.7780092593

Do these fuse links tend to be covered up? ie under the plastic wiringing loom covers. When you say small tootsie rolls, bigger in diameter than 2mm.  I'm having trouble seeing any Tootsie rolls under my hood.

It appears there are no fuse links from my solarnoid, just 2 red wires heading up to a connector a the top rear of the engine. Not good I take it.

Also on the other side of the engine bay, I've had a scout around for 2 Orange fuse links but nothing jumps out.

Although I'm new to all this Vette tinkering , I'm sure I'd be able to spot fuse link if there stand out and are actually there.

Maybe I'll get the digital camera out and see what I can photograph for you.

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Kiwi Doug

aka Harry Tasker

[QUOTE=Harrytasker]

Do these fuse links tend to be covered up? ie under the plastic wiringing loom covers. When you say small tootsie rolls, bigger in diameter than 2mm.  I'm having trouble seeing any Tootsie rolls under my hood. [/QUOTE]

They look like wire, and do tend to get wrapped in the harness with everything else. Usually they are short, maybe 6 inches long, with a crimped connector on each end.

I'll see if I can get a shot of one for you tommorrow, and post it here. They can sometimes be a little farther up in the harness, so some untaping might be needed.
I think I have wiring diag. for '78, so I'll check it, also, for locations.

btw.....nice new sig pic, Big Fish! Adams' Apple38696.9100462963

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Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Thanks heap for your help guys. It's been frustrating, I've been hanging out to get it back together so I can drive it, it's been a long time.

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Kiwi Doug

aka Harry Tasker

Here's a couple of fuse-links.

Drivers side, looking down to the outside of the master cyl.


Top of firewall, right next to the windshield wiper motor.

You'll notice, in the first pic., a wad of 'lectrical tape on one of the wires. This is where someone has removed a fuse-link, and spliced the wires back together. (red wire-to-yellow) The big, black "blob"(tootsie-roll) to the lower right of that is a fuse-link.(red wire/orange wire) This may be where your blown link(s) are.
The second pic. is two links, just to the pass. side of the wiper motor.
There are more of these comming up from the starter, but I don't have a car in the air to get pics of those, but they will look just like these. Happy Hunting! Adams' Apple38697.8204398148

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Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Thanks for those photos

I have definitely not seen any of those Tootsie Rolls on my Vette. They sorta stand out dont they. Next weekend I'll have a better look in the engine bay and may unwrap a few engine bay looms to see what I can find before I go removing my dash again.

I was thinking back to how I could have stuffed this part of the circuit. Do you think the head light switch and immediately associated wiring would have anything to do with those circuits? (heater fuse and turn sig) I replaced the headlight switch cos I stuffed my original one (vacuum and switch) as I found out when I put it back together, I had a little smoke come out from the headlight swicth/connector area. The old swich was pretty beat up to begin with.

The only other thing I think I shorted a while back was the cigarette lighter 12v cable onto a metal frame which supports the centre console. I have since insulated that cable while working.

One other thing, should I have got 14 odd volts from the solarnoid, when I measured it the other day? Is this just an effect of the internals of the solarnoid. Dont forget you are talking to a relative novice here. That may have been a stupid question

I am now an expert at removing the seats, centre console, dashboard, carpets and installing heat shielding etc and putting them back again. Though expert might be a bit much considering I created some electrical issue as a result Oh well

Thanks again for your help guys. Until next weekend.

Cheers

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Kiwi Doug

aka Harry Tasker

The headlight switch shouldn't have any effect on the heater or turn sig. circuit.

There should be 12.5(avg)volts at the starter solenoid, unless the engine is running. Then you should have around 13-14.5v.

The shorted cig. lighter could be the cause of the blown fuse-link. Does it work now, or not?
I need to get the wiring diag. to see whats what on your year. I'll check that out...

______________

Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

I've just ordered a laminated wiring diagram for my records and use but that probably wont be here for a few weeks knowing the post, and it's nearly Christmas.

My engine wasn't running when I got 14 volts on the solarnoid, I only noticed it cos it was high. I'm pretty sure I had my multimeter on the right setting. I'll check that cig lighter voltage again to see if it is still there, I haven't done since pulled it apart.

At least this is all practice leading up to maybe one day fully restoring one. I'll need a bigger garage for that though.

 

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Kiwi Doug

aka Harry Tasker