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Discussion Starter #1
Hi All,

We are replacing the original 250 in a 76 concours with a 350. Need to know if i need to replace the wiring harness as well? The previous owner had some rewiring done and the harness looks great, hate to replace it if i don't have to.
 

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Hi All,

We are replacing the original 250 in a 76 concours with a 350. Need to know if I need to replace the wiring harness as well ? The previous owner had some rewiring done and the harness looks great, hate to replace it if I don't have to.
You just need to do a good visual inspection of the existing harness and then, chances are, some wires may not be long enough to reach to different spots like possibly the oil sender wire, the water temperature sender wire, the starter solenoid and so on while some may also be too long and that's fine.

Look at all of the old connector ends and if they are questionable, replace them with either new or ones from a donor car harness.

If a wire is too short, ideally get a section of wire that can be used to extend an existing wire and have it to where it's the same gauge and color for consistency should you ever have to troubleshoot something. Nothing wrong with going from a factory blue wire to a brown wire and then back to the factory blue that would connect to something like a sender but the wire gauge needs to be the same or larger.

Something I have done before is go to a salvage yard and cut out a harness from the same era car you are working with to get wire to use instead of buying bulk wire from a supplier. Most of the time a 70's GM car will use the same gauge and color wires for different circuits so try and stay in the 70's era GM cars and don't go getting wiring out of a 2010 era as a lot was changed through the years.

When you cut the wire and splice in a new section to make it longer, try to solder the connection and then slide over and shrink down some heat shrink tubing over the connection to protect it.

If an old wire is too long you can cut out the excessive length but you can also double back or loop back the excess in the harness and then too keep things tidy, use some harness tape (not electrical tape) or even real small zip ties and then cover the whole works with other wiring inside in what they call split loom tubing.

Jim
 

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Discussion Starter #3
thanks

thanks jim,

i'm completely comfortable doing any mods (shortening or lengthening) and am OCD about making the wires match. i just wasn't sure if there was any differences in under the dash or engine compartment connections.

This is my sons car and he is paying for everything, and just 16 and not working yet, so glad he won't have to drop a couple hundred on a wiring harness. has too many other parts to spend money on.
 

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thanks jim,

i'm completely comfortable doing any mods (shortening or lengthening) and am OCD about making the wires match. i just wasn't sure if there was any differences in under the dash or engine compartment connections.

This is my sons car and he is paying for everything, and just 16 and not working yet, so glad he won't have to drop a couple hundred on a wiring harness. has too many other parts to spend money on.
There will be differences in the wiring harness depending on factory installed options but they go in a matched set. In other words if the car was originally equipped with optional gauges then under the hood there would be wires for the tachometer and then the interior/underdash harness would also be different to support the optional gauges. You cannot expect an engine harness designed for no gauges to work with an interior underdash harness setup for gauges. In your case you are just swapping motors and both will need to be setup with the proper sensors. The indash oil light could care less if the oil sender was on a 4 cylinder, a 6 cylinder, or a big or small block V8. The same for the water temp sender. The crank wire for the starter solenoid does not know if it's connected to a 6 cylinder starter solenoid or a V8 one.

If you are getting new senders for water and temperature, just make sure they are for what you have in the car (idiot lights or gauges).

Just make sure you also keep in place any fusible links.

You might also do some searches to see what shows up with wire routing to make things go smoother.

Jim
 

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Discussion Starter #5
Thanks again! he does have a base gauge cluster with idiot lights and i would like to upgrade it.

Which leads to another question - there's a 78 rally cluster for sale in the classifieds and i was wondering if it would work on his car? Based on what you said i am guessing the answer is yes, if i change out the harness, which i would have to do anyway if i wanted to upgrade.

Any experience with the "universal" harnesses? are they easy to work with or if i'm ok with wiring would it be just as easy to pillage a donor and make my own?
 

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Which leads to another question - there's a 78 rally cluster for sale in the classifieds and i was wondering if it would work on his car? Based on what you said i am guessing the answer is yes, if i change out the harness, which i would have to do anyway if i wanted to upgrade.
As far as the wiring goes, changing from the standard warning light cluster to one of the factory optional gauge clusters isn't all that difficult. It's basically a matter of re-pinning the cluster connector, changing out the temp sending unit, and making a few changes to the alternator wiring to deal with the lack of a "gen" light in the gauge cluster.

However, GM made some design changes to the Nova dash so the 1977 through 1979 instrument clusters are not a direct fit into a 1976 or earlier dash. I believe the metal dash structure stayed the same so the swap is possible. To fit the 77-79 cluster into the dash you would need to change over to a 77-79 bezel. And then you would need a 77-79 dash pad to mate up with the bezel. I think you may also need a 77-79 windshield wiper switch because the mounting points on the bezel are different. And instead of just re-pinning the cluster connector, you would have to change that too because 76 & earlier used a 12-pin plug while 77-79 have an 18-pin plug.
 

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Discussion Starter #7
wow, thanks ray. that's a lot to think about. i can't seem to find any replacement dash parts for his 76 so if it would fit we may just upgrade the entire dash to 77-8 parts.
 

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wow, thanks ray. that's a lot to think about. i can't seem to find any replacement dash parts for his 76 so if it would fit we may just upgrade the entire dash to 77-8 parts.
You're welcome. The 75 & 76 Nova dashes actually share more in common with the 69 - 74 dashes than they do with 77 - 79. So that might be another alternative to look into depending on what you need for parts and/or the style you want to go with. There were some styling changes, but for the most part, the 69-74 dash pads, instrument clusters, and bezels will be a direct fit into a 75 or 76 and have the ability to mix & match with existing 75/76 parts (unlike 77-79 where you would have to change everything over to that style so the pad/bezel/cluster all fit together).

One thing that did change was the notch for the steering column in the lower part of the instrument panel bezel. So using a 69-72 bezel in a 73-76 will leave a gap between the column & bezel unless you also change over to a 69-72 upper column hanger bracket to move the column up slightly higher.

Oh, and the factory optional gauge package that was offered in 69-74 (and 75-76) was mounted in the forward part of the console, instead of all being incorporated into the instrument cluster like 77-79. So adding that option requires a factory console, which in turn require bucket seats. But there are a number of aftermarket and homemade alternatives if you want to put all the gauges in the dash. For example, my 74 does not have AC so I put in an AC style dash pad and used the center vent opening it provided to mount 3 Autometer gauges. And bought a tachometer from Shiftworks that fits in place of the factory clock opening. There are also a number of aftermarket dash bezels available that allow you to mount a full array of gauges in place of the stock instrument cluster.
 

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wow. thanks again ray!! a lot more to think about. let me share more about what we have and see if there are any more suggestions.

its a 76 concours (according to title and vin) with bucket seats, a/c, and center console. the dash pad is trash (except the ac vents and wood grain panel - they are pristine), the bezel is also pristine - wood grain, no cracks, fading, etc., the cluster is 4 hole w/ a speedo, fuel gauge, and idiot lights.

trying to keep costs down as he is paying for this, only 16, and not working yet. if we could keep his bezel, get a 69-74 dash pad, and get the 77 cluster to fit would be the ideal situation.

the cluster is a 4 hole cluster so i am thinking i could get it to align to the existing bezel, may have to do some creative plastic work and wiring but i think i can. this is the one for sale:



not sure about the dash pads though. the 69 - 74s w/ ac only appear to have 1 vent opening and not the dual vents that his 76 has. is that more plastic work, or even doable? this isn't his, but a pic of what his looks like, same pad, bezel, and cluster, except he has woodgrain.




i am starting to think maybe he already has a 77 dash???

i will take some pics of what we have and post them this weekend
 

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i am starting to think maybe he already has a 77 dash???
Interesting! Yes, it does indeed sound like his car already has the 77-79 style dash. In which case that 78 gauge cluster you found should be a direct physical fit with just some wiring changes to make it functional. However, with that style of cluster/bezel, you'll have to stick with the 77-79 style dash pad ... the earlier year pads won't come close to fitting up correctly against the bezel.

I have heard of titles being off a year due to fact that new model years were/are introduced partway through the calendar year. For example, the 1977 models were available during the later part of 1976. So if someone bought a 77 model in late 76, it wouldn't be unheard of for the title to have been typed up as a 76. Although with the VIN also indicating a 76, it sounds like someone has already done some parts swapping to change over to the 77-79 style dash.
 

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Prezie,
That is indeed a 77-79 dash. Easy to tell because they are flat on the top all the way across. the 75-76 dash curves down in the middle and over to the passenger side.
You can see what we did to our 76 on page 10 of our build.
https://www.stevesnovasite.com/forums/showthread.php?t=424858&page=10

On Page 13 you can see the completed dash.

There are some pictures of the dash all apart so you can compare the metal structure of yours to ours on Page 15 and 16 where we are working on the AC.
 
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