TAC Tech => Mechanical => Topic started by: roadking77 on April 03, 2021, 08:56:11 AM
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How hard is it to hook up the tach?
1977 400 auto trans
The 2 things on my car that have never worked (since restoration) are the speedo and the tach. I would like to get these sorted before the car season starts, hopefully TODAY! :grin: :grin: :grin:
Seriously, if the tach is something that my moderate skill level can hook up thats fine, otherwise Im taking the car to the shop this week for a seasonal service, oil change, etc. and would like for them to get it working.
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You can do it!
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Kerry, it's very easy and you can do it. I wish my write up was still here to use as a referance, but it's very easy especially if the car had one already.
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Hi Kerry - Shouldn't be too hard. I have a 78 TA, TH350. The cable from the transmission just pops into the back of the dash gauge with a few retaining clips. A little pressure to push it on and you should be all set. I have seen some of the work you do, this is pretty simple in comparison. I sent my gauges out for to http://www.autoinstruments.com/ (http://www.autoinstruments.com/) for repair and to reset the mileage to 000000. As mentioned by Not a TA - you can do it ;)
If you get stuck, LMK, I will snap a few pics for you.
-Tony
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Kerry, I have a couple sets of gauges. I'll try to remember to get one tomorrow an snap some pictures to help show you what the others are talking about.
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I've never done it, but I would assume there would be just 4 wires. One for tach signal, ignition, lights, and ground. The signal wire comes from the tach terminal on the HEI. If you have an MSD ignition, the signal would come from that.
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Actually just two wires. It grounds through the cluster. The lights are part of the cluster.
The wiring wasn't part of the harness until 1980. Prior to that, they had an add-on. The add-on looked like this. The power supply plugged into the front of the fuse box
(http://www.firebirdtransamparts.com/techinfo/harness/optionwire/tach.jpg)
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Joe,
Thanks! That is perfect and makes sense about the harness and 1980. When I restored the car a few years ago I was gonna get a whole new harness, just because. But I read one of your statements somewhere that the wire isnt just going to go bad and figured what the heck and wing it. I was quite pleasantly surprised when everything worked like it should. Except for the tac and speedo. I knew the speedo was a mechanical connection that was disconnected at the cruise servo, but the tach had me baffled.
Now, if I can find some time to get it tachled.
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(https://live.staticflickr.com/65535/51098044135_8c16bf7866_z.jpg)
Here is the back of the instruments. I crudely circled the two plugs and the speedometer hookup. I figured a picture might help others if searching for help.
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Thanks Luke, def helps.
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Not to derail your thread Kerry
Joe,
What is the white plug in the distributor line? Fuse? Or some kind of signal thighy?
I don't have that on my car.
I currently have a issue, that then I connect my Tach on the negative of the coil, then it interferes with the temp gauge reading. The temp gauge jumps to max. Installation instructions says to connect tach wire to negative coil. Simple as that.
The two wires go through the same hole the firewall. It was suggested to me this morning that I should rather separate the two through different areas of the firewall. My instrument cluster is not fully hooked up yet. I have only connected essentials.
Any ideas?
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There's a fuse in there in the signal wire. The appearance of it changed sometime in the 70's. Maybe they hoped it would prevent the tach from being burned out by something, I don't know.
For the specific problem of the temperature gauge. The harness here in question doesn't touch anything or even go close enough to anything to touch it. It would be really hard to see how that would affect another gauge. When the tach is powered up, the tach and the "cold" direction on the temperature gauge ground through the same circuit, but that circuit goes everywhere and grounds everything. The oil gauge also is grounded through there in a single screw.
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There's a fuse in there in the signal wire. The appearance of it changed sometime in the 70's. Maybe they hoped it would prevent the tach from being burned out something, I don't know.
Did they ever not have a fuse to your knowledge? Reason I ask is the manual makes reference to an inline fuse on the cruise circuit for my 77 but I’ve never been able to find one. I also have another complete harness out of another bird and it also lacks a fuse. I’ll have to look and see if my tach wiring has a fuse now cause I’m curious.
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I think they did away with the fuse in 79 or 80. I have forgotten a lot of what I knew about this stuff.
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I'm sure you have forgotten more than I even know! :shock:
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There's a fuse in there in the signal wire. The appearance of it changed sometime in the 70's. Maybe they hoped it would prevent the tach from being burned out by something, I don't know.
For the specific problem of the temperature gauge. The harness here in question doesn't touch anything or even go close enough to anything to touch it. It would be really hard to see how that would affect another gauge. When the tach is powered up, the tach and the "cold" direction on the temperature gauge ground through the same circuit, but that circuit goes everywhere and grounds everything. The oil gauge also is grounded through there in a single screw.
I'm starting to wonder if it's not a ground issue.
The cluster is grounded to the metal part at the steering column. As far as I know this is a common ground. Then I have a ground from the battery to the top of the intake where the alternator sits.
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I ordered a new Tach harness, as far as I know there wasnt one there when I put stuff back together. I'll let y'all know how things work out once I get it.