factory tach install will it work?

Ok so has anyone got these tachs to work yet? I'm waiting to pull the trigger

yes, mine is working just fine with the dakota digital DS1 module wich gets its input from the Alternator. I am using the LMC tach

Thank you... What did you do with the fuel gauge?

I purchased the small fuel gauge from LMC and moved it to one of the small holes. I am using a civy gauge cluster. I moved the 24volt meter to the top left corner. i have the civy water temp gauge to right of meter. The fuel gauge is in the bottom left corner and the oil presure guage is next to that. My gen one and gen two have been moved to the lights in the bottom of the fuel gauge and then put red led's in the cluster.

Rich - I obtained one of those 4000 RPM Medium Duty Truck tachs with the small fuel gauge and plan to begin installation soon. I will abandon the seat belt and brake warning lights and modify the fuel gauge wiring so it will work.

It would be very helpful if you could post the Dakota Digital DS1 module information and where the best place to buy it.

Thanks in advance.

http://www.dakotadigital.com/
I bought it on line. the directions are easy to follow. I just spliced into the current alternator lead which I believe only goes to the diagnostic port. getting the small fuel gauge into the standard cucv cluster is going to take some cutting and some work getting it to screw into place It sits in the cluster at an angle. Using a civy cluster it will screw in without any mods but then you dont have the holes for the other lights. I decided to go with the civy cluster and thus I moved other things around. In the speedo I have the 4x4 light and a check engine light. I kept the existing sending units and installed the addtional sending units for the guages using some fittings and T's. My check engine light comes on wtih either of the following: low coolant, low oil presure or high water temp. This way if I am not paying attention to the gauges, I still get a light also.

richingalveston said:

I purchased the small fuel gauge from LMC and moved it to one of the small holes. I am using a civy gauge cluster. I moved the 24volt meter to the top left corner. i have the civy water temp gauge to right of meter. The fuel gauge is in the bottom left corner and the oil presure guage is next to that. My gen one and gen two have been moved to the lights in the bottom of the fuel gauge and then put red led's in the cluster.

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Very trick setup!!!!

I'm guessing this is the Dakota digital module:

http://www.summitracing.com/search/...nator-tachometer-interface-units?autoview=SKU

yes that is the same module I purchased from dakota digital. appears to be the same price.

I've been researching this on the web.... It seems that the c 60 tach fuel combo is the easiest they say the fuel gauge uses the existing contacts for the old fuel gauge and you have to cut a hole in the back of the cluster for the tach connection

jsd563 - due to career duties, I will not be able to install my C-60 4000 rpm GM tach until later in the spring. I will post photos of the process as I get into it.

richingalveston said:

I purchased the small fuel gauge from LMC and moved it to one of the small holes. I am using a civy gauge cluster. I moved the 24volt meter to the top left corner. i have the civy water temp gauge to right of meter. The fuel gauge is in the bottom left corner and the oil presure guage is next to that. My gen one and gen two have been moved to the lights in the bottom of the fuel gauge and then put red led's in the cluster.

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Where did you get the red LED lights at? How many did you need and what style were they?

I appreciate it! I love the red!

www.Superbrightleds.com I got this site from another member here on the forum. I do not have the model #s of which ones I used with me but I can post them tomorrow. The leds work good but they do not dim. They are either on or off with the dimmer knob. With the bulbs I used most were a 5 led bulb but in two locations I used a larger 25 led bulb which made the red more even. I also painted the inside of my cluster with chrome paint and the back side of the black face plate chrome, which is normally light blue. I also wrapped the back of all of my gauges with metal tape and cut some of the excess metal from the edges of the guages. I basicly made the inside of the cluster a chrome finish to enhance the light distribution. the red works good, it is easy on the eyes and does not need to be dimmed. My 24volt meter was moved to the top left hole in the cluster and they also had a red led bulb for the guage (it is a different socket). I also purchase LED bulbs for my tail lights and side marker lights and reverse lights. they work great also. In order to not have to use a different flasher, I left the front marker lights (under the headlights) with regular bulbs. All other lights have been changed to LED and every thing works great. I wanted to reduce the amp load as much as possible on the old wiring to help make it last longer.

Gen 1 and 2 bulbs must remain regular bulbs but all others can be changed to LED. I even changed the wait light, water in fuel light, the high beam indicator and the heater control panel bulbs to red LED's.

You would not need as many LED bulbs if you are doing the stock cluster. I have a civy cluster with all gauges so it uses a few more led's than what the stock cluster would use.

Anyone actually get this to factory 4000 rpm tach with gauge to work? I just put one in and it reads about 1/4 the speed it should. Open to suggestions....

Winston Wolf said:

Anyone actually get this to factory 4000 rpm tach with gauge to work? I just put one in and it reads about 1/4 the speed it should. Open to suggestions....

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i have one of those 4000 rpm tachs but haven’t installed it yet. If I remember correctly the plug on the back has 3 wires, one is a 12v hot, another for the tach signal, and the third as a ground. I’d suggest you make sure it is grounded properly. Also, there is a little switch on the back which I assumed would be to change the signal from a 6 cylinder to an 8 cylinder.

Sharecropper said:

i have one of those 4000 rpm tachs but haven’t installed it yet. If I remember correctly the plug on the back has 3 wires, one is a 12v hot, another for the tach signal, and the third as a ground. I’d suggest you make sure it is grounded properly. Also, there is a little switch on the back which I assumed would be to change the signal from a 6 cylinder to an 8 cylinder.

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The “switch” you are mentioning connects 2 terminals on the board or none, there is a A and a B setting, along with taking out the switch/bridge. I’m not sure why a tach that works off the alternator would care if it’s an 8 or 6 cylinder, the alternator wouldn’t know or care. It doesn’t seem to make a difference what position it’s in. It doesn’t register much over 500 rpm while revving up. Both the board and the plastic backer are marked ‘coil’. Wonder if this is a gas version...? I talked to the tech guy at Dakota Digital, and he thinks their diesel tach adapter won’t work with the diesel tach (if this thing really is an alternator/diesel tach). He said it might work for a while and then fry the tach. I ordered one anyways to see if that makes it work. Guess I might be the first one to actually try this.

Winston Wolf said:

The “switch” you are mentioning connects 2 terminals on the board or none, there is a A and a B setting, along with taking out the switch/bridge. I’m not sure why a tach that works off the alternator would care if it’s an 8 or 6 cylinder, the alternator wouldn’t know or care. It doesn’t seem to make a difference what position it’s in. It doesn’t register much over 500 rpm while revving up. Both the board and the plastic backer are marked ‘coil’. Wonder if this is a gas version...? I talked to the tech guy at Dakota Digital, and he thinks their diesel tach adapter won’t work with the diesel tach (if this thing really is an alternator/diesel tach). He said it might work for a while and then fry the tach. I ordered one anyways to see if that makes it work. Guess I might be the first one to actually try this.

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What I had intended to do, and still plan to do, is to temporarily wire the tach with it laying on a bench beside the truck and the truck running. I actually have 2 of these things, 1 older tach still mounted it a mid-1980’s cluster, and another NOS unit still in its GM box. Both tachs appear to be identical. I have the original plug and harness that came with the older unit and it is obvious that one wire went to ground due to the surviving ground fitting on the end opposite the plug. I still think your ground may be suspect. Also, where are you obtaining the tach signal? The brown wire from the passenger alternator goes to the ICE plug in the cab and provides the tach signal to the ICE testing instrument. I planned to temporarily tap this wire when I bench-test my 2 tachs to see if either would work correctly. There’s just got to be some way to make it work. This thread has reenergized my interest and I will try to find time to perform the bench test on my 2 tachs in the next few days. I will post my results.

I have the original plug in the tach, and it's clearly marked/labeled how to hook it up. 12v-gnd-coil. I'm grounded directly to the grounding bar, so I'm certain that isn't the issue. I'm taking the signal off the alternator, tapped in right out of the alternator plug. I have been using this signal wire for years to drive my VDO tach. I currently reinstalled the VDO tach along with the factory one, and the VDO still works as it should.

This tach came out of a 1990 Topkick, but I'm not sure what engine it had.

Can you confirm on your 2 units , where the tab/switch is at? A-B-or not there.

My my guess is that these came in the trucks with the Cat 3126, 3116 and 3208 and the alternators may have been set up for 3-4 times as many pulses as the 6.2 alternator, thus the slow reading.

Maybe the dakota digital box will do something...

In doing more research, the 3100 series cat engines drove the tach from the engine control module. I'm guessing that these tachs might be set up for way more pulses per rev than a "standard" diesel alternator tach.

So, I tried the Dakota Digital box, and it doesn't work with the 4k rpm tach. I can't get a readout over probably 100 RPM. I tried all kinds of settings and even called in to tech support to try and get some assistance. I hooked the tach back up without the Dakota box, and played with the A/B setting on the back (I soldered 3 jumper wires to the terminals so I could change the setting without taking the gauge out.) It looks like the highest reading is probably with no jumper, but that may be the same as position A, not enough to tell the difference. The tach is reading 250 RPM at 1000 RPM, so it's about 25% of actual RPM. I think the best way is going to be to increase the signal frequency from the alternator. I'm not an electronics expert, so I'll have to do some research on that and make my own thing most likely.