Tachometer replacement thoughts

[Turbo4whl]

The tach with inset fuel gauge is probably from a heavy duty GM truck (don’t recall the exact model), since it only goes to 4K rpm. The HD truck cluster is the same physical size, and apparently can be adapted to a squarebody.

The tach with the fuel gauge is from the square body medium duty trucks. The 4000 RPM is a diesel engine. The V8 gas engines have a 5000 RPM combo gauge. It is not very hard at all to replace your large fuel gauge with the combo gauge.

You can use your old cluster. Need to cut a hole in the back for the combo gauge to fit. Need to remove the fuel sender wire from the the large gang plug. From there you just need wire and connectors.

Both new gauges need ign pos. and ground wired to them. They each need their 3rd wire. Sender wire to th fuel gauge and a new wire run to the dizzy for the tach.

Tape the unused contacts on the print and put it back in place for the dash and turn lights.

 

[SirRobyn0]

The tach with the fuel gauge is from the square body medium duty trucks. The 4000 RPM is a diesel engine. The V8 gas engines have a 5000 RPM combo gauge. It is not very hard at all to replace your large fuel gauge with the combo gauge.

You can use your old cluster. Need to cut a hole in the back for the combo gauge to fit. Need to remove the fuel sender wire from the the large gang plug. From there you just need wire and connectors.

Both new gauges need ign pos. and ground wired to them. They each need their 3rd wire. Sender wire to th fuel gauge and a new wire run to the dizzy for the tach.

Tape the unused contacts on the print and put it back in place for the dash and turn lights.

Thanks for that. Totally different from something I read somewhere else, or I'm simply misremembering, either way it's apricated and doesn't sound to hard.

 

[Turbo4whl]

Oh, one last thing. You need to remove the resistor from your original fuel gauge and replace the one on the new gauge. Different colors are different resistances

 

[scrap--metal]

I like the gauge but not the installation. I can see the appeal to do it like that, but my current tach is attached to the dash pad screw by the ash tray and that location is fine for me.

Rob, do you have a picture of your current tach on the dash? I'd like to see it.

A friend gave me an aftermarket tach (cheap "Sun Pro" maybe?) that will eventually go in my K20. It's still sitting on my bench because I can't decide where to mount it. Personally, I've never been a fan of the steering column or top of dash pad mounting positions. I think I'd be more inclined to put it down under the radio at the lower edge of the dash, but your dash pad screw sounds like a good alternative.

Please post a pic. Also, what diameter tach is it?

 

[SirRobyn0]

Rob, do you have a picture of your current tach on the dash? I'd like to see it.

A friend gave me an aftermarket tach (cheap "Sun Pro" maybe?) that will eventually go in my K20. It's still sitting on my bench because I can't decide where to mount it. Personally, I've never been a fan of the steering column or top of dash pad mounting positions. I think I'd be more inclined to put it down under the radio at the lower edge of the dash, but your dash pad screw sounds like a good alternative.

Please post a pic. Also, what diameter tach is it?

Ok pics first then I'll tell you about it and why I picked that location.

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So I picked that location for the tach before I had the trans temp gauge. At the time I wasn't sure if I'd keep it there so I didn't want to put any holes in the dash. I removed the factory screw and installed a longer one for the tach to mount to. It's been great and I love the location. It's not obscured by the steering wheel at all. Like you I thought about going below the radio, but I had two concerns with that. One is I have switches mounted there, and the other thing is that the steering wheel would obscure it. The tach measures about 3 3/8". I've actually been very happy with both the location and the tach itself. If I replace it with another aftermarket unit it'll go in the same location for sure.

 

[scrap--metal]

@SirRobyn0 thanks for the reply and the picture. The tach destined for my k20 is the same size, so it's good for reference. I've honestly never considered that location before.

My only concern with that spot is riding three deep on the bench seat. It doesn't happen often, but maybe one or twice a year goose hunting and it did happen on a 5+ hour trip to the BWCA one year.

The tach might be in the center passenger's left knee. Right?

 

[SirRobyn0]

@SirRobyn0 thanks for the reply and the picture. The tach destined for my k20 is the same size, so it's good for reference. I've honestly never considered that location before.

My only concern with that spot is riding three deep on the bench seat. It doesn't happen often, but maybe one or twice a year goose hunting and it did happen on a 5+ hour trip to the BWCA one year.

The tach might be in the center passenger's left knee. Right?

I don't think it would be a problem at all. So from 1980 until 1996 my Dad had a 78 C20 my parents and me took it camping and to the ocean lots of times, 4 plus hour trips and his truck was a 4 speed, so whoever was in the center had to be mindful of the shifter, but we did it.

Now for our trucks, with automatics and tach in that location. So I have a removable floor cup holder and I do not ride three very often at all but do it from time to time when pulling in hay. I've never had someone hit the tach. Honestly they'd need to have super long legs or slouch a lot. It just so happens that I needed to go out and get something out of the truck when I saw your message so I hopped in the center seat position, it's dark so I had to use flash but this should give you an idea. I guess if you had a really rambunctious guy in the center seat it's possible but I'm 6 foot, and weigh a little north of 250 so I'm a pretty big guy and clear them getting in and out and lifting my feet over the cup holders. Anyhow pictures.

First pic I'm just sitting naturally, second pic I'm kind of squeezing my legs together like you might have to as the center passenger.

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Using that pre-existing hole you can always move it later if it's an issue, and you would be leaving an scar on the truck if that is important to you.

 

[SirRobyn0]

As you can see I've turned my ash tray into a power center, so I just have the tach wires run right in there so there is no wiring for a third person to catch. All the wires you see in the pictures are phone charger, laptop charger and GPS, the tach makes a great place to coil that stuff around when not in use.

 

[scrap--metal]

Awesome PICTURES! Thank you! You've gone above and beyond my expectations, @SirRobyn0. I will have to go mock it up in my truck and give it some thought. Since I do not have any switches down low like you do (dump bed switches???) that's the other location I'm considering.

I have an aftermarket tach down low on the bottom of the dash in my Monte Carlo, and have grown very accustomed to it.

The center hump is a little bigger on my K20 because of the 4wd, but I think the story of your folk's C20 with a 4-speed is relatable.

 

[Turbo4whl]

I don't think it would be a problem at all. So from 1980 until 1996 my Dad had a 78 C20 my parents and me took it camping and to the ocean lots of times, 4 plus hour trips and his truck was a 4 speed, so whoever was in the center had to be mindful of the shifter, but we did it.

Now for our trucks, with automatics and tach in that location. So I have a removable floor cup holder and I do not ride three very often at all but do it from time to time when pulling in hay. I've never had someone hit the tach. Honestly they'd need to have super long legs or slouch a lot. It just so happens that I needed to go out and get something out of the truck when I saw your message so I hopped in the center seat position, it's dark so I had to use flash but this should give you an idea. I guess if you had a really rambunctious guy in the center seat it's possible but I'm 6 foot, and weigh a little north of 250 so I'm a pretty big guy and clear them getting in and out and lifting my feet over the cup holders. Anyhow pictures.

First pic I'm just sitting naturally, second pic I'm kind of squeezing my legs together like you might have to as the center passenger.

You must be registered for see images attach

You must be registered for see images attach

Using that pre-existing hole you can always move it later if it's an issue, and you would be leaving an scar on the truck if that is important to you.

Look at those legs, you must work on a farm.

 

[SirRobyn0]

Awesome PICTURES! Thank you! You've gone above and beyond my expectations, @SirRobyn0. I will have to go mock it up in my truck and give it some thought. Since I do not have any switches down low like you do (dump bed switches???) that's the other location I'm considering.

I have an aftermarket tach down low on the bottom of the dash in my Monte Carlo, and have grown very accustomed to it.

The center hump is a little bigger on my K20 because of the 4wd, but I think the story of your folk's C20 with a 4-speed is relatable.

When I installed the tach I think there was only one switch down there to the right of the steering column. What I didn't like about that was for me the steering wheel obscured it to much.

I can't find a picture down low of my dash other than this one. So the black box on the left of the picture is the trailer brake controller. To the left of that out of the frame is the dump bed switch. It's all alone over there so I don't hit it inadvertently. Going from left to right with the switches you can see. Tank switch, it's originally a single tank truck, so it's got an aftermarket tank switch setup. Next fog lights (hella 550's, and yes I love them). Next power switch for trailer brake controller, and the last one on the right is a 2 second wiper delay switch.

Wherever you decide to mount yours it would be cool to see pics.

 

[SirRobyn0]

Look at those legs, you must work on a farm.

I know right! They have seen their share of work! You ever buck hay in shorts? Now there is a good time lol

 

[idahovette]

@SirRobyn0 ^^^^did that ONCE in cut-offs(that's what we used to call them, not shorts)!! my legs were scratched, bleeding and sore for weeks!!!!

 

[SirRobyn0]

@SirRobyn0 ^^^^did that ONCE in cut-offs(that's what we used to call them, not shorts)!! my legs were scratched, bleeding and sore for weeks!!!!

To me that's the worst part of bucking hay. It's not the physical work, or at least it didn't use to be, when my body was better. To me the worst part was it's gotta be done when it's hot out and you gotta have everything covered. Jeans, and flannel. Now when I do hay I'm just the driver I have to have someone else do the work, but that's the way it goes. I remember having cut-offs too.

 

[Albrigap]

Last summer I replaced the big gas gauge with a tach and moved the gas gauge to where the clock was.
I tried to order the "kit" to do this from LMC. It was backordered for 6 - 8 months. I finally got tired of waiting and ordered all the individual pieces which "amazingly" they had. Paid about $100 more than the "kit" price. I ended up having to get the back panel also as the new, small gas gauge didn't mount in the place where the clock was on the old one.
You will need the correct printed circuit for sure.

I have pics and can list the items I bought if anyone needs it. I have an '83 GMC Sierra Classic SB.

I got tired of not knowing how much fuel was in each of the duel tanks on my 81 diesel. So I put two fuel gauges, side by side, with the short needles off the oil pressure and other gauges into the big fuel gauge. I used model railroad lettering to add the empty/full, etc on the new gauges plus a Left/Right under each gauge. A bit of wiring as I had to run one wire from the tank sender and I was in business. So the two gauges now show how much fuel is in the left and right tank in real time. All you have to do is look at the tank selector switch to know which tank you are drawing from.