HO speedometer question

[DirtyComanche]

Search failed me - Is the electric speedometer on the HO more or less a standalone component, as in as long as you have the cluster and the little tach gen box that goes on the speedo drive and a couple wires it will work?  Or does it integrate with something like the PCM/ECM/whatever other magical boxes and miles of wiring?

 

I want to use one for a swap rather than a cable drive simply so I don't have to route a cable.  It just seems like a better solution.  Yes Hornbrod, I am admitting that certain Chrysler components are better.

[Jeep Driver]

I'll take a stab at it-

 

Since you can get a speed sensor code........I'm pretty certain that the speed sensor input goes to the TCM then the PCM. 

 

A primary reason that I'm going GPS when I order my new cluster. Should also free me up to use a later TC, no speed sensor, I'll have to look into the compatibility.

[DirtyComanche]

I might look at the HO wiring diagrams later today then.

[kryptronic]

I doubt you're going to have an easy time with it.  The HO cluster plugs directly into the dash wiring harness, which routes to the computer, and has wiring going back to the NP231.  Your NP231 has provisions for a cable right now, that would need to be converted to an HO/electric unit.  I am pretty sure the speedo gears are the same cable vs. electric in the NP231, but you'll be missing the wiring back to it (you have a cable running there now).  I couldn't tell you offhand if the wiring runs right to the harness or through the computer first.  Just my thoughts, could be very wrong.

[HOrnbrod]

The speed sensor does feed the TCU and ECU, along with the distance sensor. It's processed along with other inputs then a variable square wave is sent to the speedo. How it happens I have no clue. The speedo is definitely not stand alone. Good idea though Dirty. The 91-92 is unique with a 3-wire speed sensor; it was changed to the more common 2-wire in 93.

 

You could always work in an aftermarket unit somehow........

[DirtyComanche]

1 hour ago, HOrnbrod said:

You could always work in an aftermarket unit somehow........

 

Yeah, Dakota Digital has various signal conversion boxes, along with some other companies.  That said, it's probably not worth it then.  But I could look into it a bit more.

 

IMHO the factory cluster looks and fits better than most other options.  I spent some time trying to fit a GPS speedo and matching tach into the stock cluster and was never happy with the results.

[HOrnbrod]

Back when I was playing with XJ/MJ dash gauges I had an old function generator that would put out a square wave @ ~ 2V peak-to-peak or so. I used that as a input to the HO speedos on the bench and got variable indicated speeds by changing the frequency of the square wave. This was just an ops check, but I had no idea how to calibrate the speedo based on the inputs.

[DirtyComanche]

4 hours ago, Jeep Driver said:

I'll take a stab at it-

 

Since you can get a speed sensor code........I'm pretty certain that the speed sensor input goes to the TCM then the PCM. 

 

A primary reason that I'm going GPS when I order my new cluster. Should also free me up to use a later TC, no speed sensor, I'll have to look into the compatibility.

 

Who are you ordering a cluster from?

[DirtyComanche]

1 hour ago, kryptronic said:

I doubt you're going to have an easy time with it.  The HO cluster plugs directly into the dash wiring harness, which routes to the computer, and has wiring going back to the NP231.  Your NP231 has provisions for a cable right now, that would need to be converted to an HO/electric unit.  I am pretty sure the speedo gears are the same cable vs. electric in the NP231, but you'll be missing the wiring back to it (you have a cable running there now).  I couldn't tell you offhand if the wiring runs right to the harness or through the computer first.  Just my thoughts, could be very wrong.

 

This wouldn't be for my 88, but if it was easy enough to do I would ditch the cable setup in both it and my XJ in a heartbeat.  The early electric speedometers use a little signal generator box that screws into the cable drive on the tcase, so it's easy to add them to any tcase that uses the 7/8th inch (IIRC) cable drive.  Obviously there is pin differences between the Renix and HO cluster, since the Renix doesn't have any provisions for an electric speedometer, but one reasonably could overcome this by using a mismatch of components or splicing some extra connections in.  Wires could be added to the vehicle as needed, it could just be done on a pegboard as a separate harness and then installed.

 

Anyways, since it appears the TCU or ECU likely modifies the output, there is not likely an easy way to make it work.  Unless like I mentioned, somebody sells a signal converter for this.

[Jeep Driver]

3 hours ago, DirtyComanche said:

 

Who are you ordering a cluster from?

This is the style I'm looking for, only 6 gauges of course. 

http://newvintageusallc.mybigcommerce.com/

 

 

[DirtyComanche]

14 minutes ago, Jeep Driver said:

This is the style I'm looking for, only 6 gauges of course. 

http://newvintageusallc.mybigcommerce.com/

 

 

Thanks for the link, I found a totally unrelated product that they make which will probably solve all sorts of problems on my Gladiator build.

[Rockfrog]

 
Thanks for the link, I found a totally unrelated product that they make which will probably solve all sorts of problems on my Gladiator build.

Been busy a while, but with regards to the HO speedo/VSS ... 91/92 used a standalone sensor, which mated to the same mechanical drive as the earlier XJ/YJ/MJ's ... After 93 ... It then routes through the PCM and then gets sent to the speedo.
This is what I found in my earlier research on the subject ... While working to eliminate my Speedo cable and run a more common HO cluster. Just have to get around to mapping the 88 cluster pinout and the HO pinout yet (this was back when I lost my job last year so it all got shelved).

Sent from my SM-G930W8 using Tapatalk

[DirtyComanche]

2 hours ago, Rockfrog said:

Been busy a while, but with regards to the HO speedo/VSS ... 91/92 used a standalone sensor, which mated to the same mechanical drive as the earlier XJ/YJ/MJ's ... After 93 ... It then routes through the PCM and then gets sent to the speedo.
This is what I found in my earlier research on the subject ... While working to eliminate my Speedo cable and run a more common HO cluster. Just have to get around to mapping the 88 cluster pinout and the HO pinout yet (this was back when I lost my job last year so it all got shelved).

Sent from my SM-G930W8 using Tapatalk
 

 

Interesting.  I have one of the 92 signal generator things around somewhere, it was the type I was planning on using.  I didn't realize they were only 91-92.  So if it doesn't route through the PCM in those years then it should work.

[Rockfrog]

 
Interesting.  I have one of the 92 signal generator things around somewhere, it was the type I was planning on using.  I didn't realize they were only 91-92.  So if it doesn't route through the PCM in those years then it should work.

Yeah, from what I found they send a straight signal, whereas the later 93+ put out a signal the PCM interprets, and then sends out the same signal pattern as the earlier sensor does. This is all going off memory but from what I was finding it was a doable thing.
Problem with finding information is piecing together all the little bits ... Seems only you and me are interested in doing this ...

Being that speedo cables are still readily available, we're likely on our own on it.

Sent from my SM-G930W8 using Tapatalk

[HOrnbrod]

22 minutes ago, DirtyComanche said:

 

Interesting.  I have one of the 92 signal generator things around somewhere, it was the type I was planning on using.  I didn't realize they were only 91-92.  So if it doesn't route through the PCM in those years then it should work.

 

I followed the speedo input signal wire back earlier today in my 91 FSM manuals. It went eventually to the ECU. Check it out - I could definitely be mistaken as it went through several pages of wiring diagrams before it got to the ECU....

[Rockfrog]

 
I followed the speedo input signal wire back earlier today in my 91 FSM manuals. It went eventually to the ECU. Check it out - I could definitely be mistaken as it went through several pages of wiring diagrams before it got to the ECU....

That's where the difference is, the 91/92 ECU's still need/use speed sensor input, but the speedo reads the signal in the the same way as the ECU does. To make it simple imagine the signal wire as a 'T' one side goes to speedo, other goes to ECU (yeah, that's seriously simplified as you found out) .
The later 93+ routes from the VSS, directly to the ECU, then the signal is translated to one the speedo can generate a reading from.
From memory, it was all to do with a waveform change in the ECU that coincided with the newer 3 wire all in one VSS. Same idea as a Renix vs HO CPS when you get down to it. Now imagine if he ECU was translating the HO signal back into Renix speak and that's the general idea of what's going on.

Sent from my SM-G930W8 using Tapatalk

[DirtyComanche]

8 minutes ago, HOrnbrod said:

 

I followed the speedo input signal wire back earlier today in my 91 FSM manuals. It went eventually to the ECU. Check it out - I could definitely be mistaken as it went through several pages of wiring diagrams before it got to the ECU....

 

I'll look into it some more.  I don't have a 91/92 FSM but I'm sure I can find one.  There is potential that even if it does go through the ECU that it will still work without being routed through it.

[HOrnbrod]

I'll look into it some more too. Have never fully understood how my speedo worked - it's definitely unconventional. Rockfrog has cleared it up a bit. 

[Rockfrog]

I'll look into it some more too. Have never fully understood how my speedo worked - it's definitely unconventional. Rockfrog has cleared it up a bit. 

I'll see if I can find the info again, wife's giving me "the eye" so not tonight.
What I found made me pretty positive it was doable, but needed a 91/92 mechanical adapted VSS to do it. From what I remember that was the critical part to the equation.

Sent from my SM-G930W8 using Tapatalk

[Rockfrog]

Ok, so a couple hours of scouring nets this little tidbit ....

The 2 wire, mechanical adapted 97 /92 VSS ... IS NOT ... A critical need to make this work. The three wire fully integrated VSS will work just as well. They both produce the same 8 pulses per second signal. Just one has a ground signal, the other (3 wire) works more like a traditional sensor (power, ground, signal out).

 

Only the 97+ CCD bus clusters supply the signal to the speedometer directly from the ECU.

 

The 96 and earlier, splice off to the speedo just before the ECU. So although the circuit does terminate at the ECU, it is not required the for speedometer to function and it has it's own separate secondary slave circuit.

 

Short version ... Run a dedicated circuit from the VSS (pick you flavour, 2 wire or 3 wire and spool accordingly), and supply the signal lead to the correct pin on the cluster and bingo, Bob's your uncle.

 

Now gimme a bit to deal with finding the pinout diagrams again. I have the paper 89 FSM sets (4 books) so the Renix cluster and wiring is easy.

Just need to find the pinout diagram for the HO clusters. Then match leads and generate a splicing/wiring plan.

 

Way more info out there now it seems, being that more and more people are swapping HO era wiring harnesses and motors into YJ/XJ/MJ vehicles (most of the VSS info came from YJ based thread discussions). And search engines seem to be getting better at zeroing in .... Or it's just that my google-fu is strong today. So, expect be to pull duds all day next week.

 

Luckily all this never happened on Facebook, so the info is still fairly easily-ish searched out if you get lucky with the right keywords.

 

Based on this, a simple battery driven circuit can be created to test function with a power drill which will then identify as a Transmission from then on (hey, it's apparently the latest thing) not sure how the VSS will feel about it, but sometimes ya just gotta quash a few feelings.

 

 

 

 

 

Sent from my SM-G930W8 using Tapatalk

 

 

 

 

[HOrnbrod]

Nice work Rockfrog - looks like a standalone HO speedo is doable electrically. Would be a great mod to dump the speedo cable for the Renix people. I'll dig around thru my 91 Electrical Manual and see if I can find the complete VSS-to-speedo gauge signal path. Pics of the HO speedo below. I don't remember if it will physically mount in the Renix gauge housing easily or not. Look like it will?

[DirtyComanche]

Yeah, I think it will fit the Renix housing.  I will have to see what I can scrounge up for parts and try doing a trial on this.  Very interesting all around though!

[Rockfrog]

Yeah, I think it will fit the Renix housing.  I will have to see what I can scrounge up for parts and try doing a trial on this.  Very interesting all around though!

I only have the one Renix cluster (currently in my 88).

I think I tried to swap one a while back ... Way back when I first started swapping guages about.
Only issue I really saw was the fuel guages, totally different mounting between the two.

If I can get the speedo to work, I may go the aftermarket (probably Equus since I already have some) and just run stock speedo/tach/fuel (unless I can find a reasonably priced and compatible fuel Guage). Hell, may eventually go full Guage set down the road. But that's a long way down the road. For now, I plan to work on the speedo conundrum and then the fuel Guage (I do have an HO XJ sender/pump assembly I can monkey with).

Sent from my SM-G930W8 using Tapatalk

[Rockfrog]

I only have the one Renix cluster (currently in my 88).

I think I tried to swap one a while back ... Way back when I first started swapping guages about.
Only issue I really saw was the fuel guages, totally different mounting between the two.

If I can get the speedo to work, I may go the aftermarket (probably Equus since I already have some) and just run stock speedo/tach/fuel (unless I can find a reasonably priced and compatible fuel Guage). Hell, may eventually go full Guage set down the road. But that's a long way down the road. For now, I plan to work on the speedo conundrum and then the fuel Guage (I do have an HO XJ sender/pump assembly I can monkey with).

Sent from my SM-G930W8 using Tapatalk

I do remember the clear covers/Odo pin locations being an issue. But honestly can't remember if I tried swapping the speedo itself or just the clear covers ...

Sent from my SM-G930W8 using Tapatalk

[DirtyComanche]

7 hours ago, Rockfrog said:

I only have the one Renix cluster (currently in my 88).

I think I tried to swap one a while back ... Way back when I first started swapping guages about.
Only issue I really saw was the fuel guages, totally different mounting between the two.

If I can get the speedo to work, I may go the aftermarket (probably Equus since I already have some) and just run stock speedo/tach/fuel (unless I can find a reasonably priced and compatible fuel Guage). Hell, may eventually go full Guage set down the road. But that's a long way down the road. For now, I plan to work on the speedo conundrum and then the fuel Guage (I do have an HO XJ sender/pump assembly I can monkey with).

Sent from my SM-G930W8 using Tapatalk
 

 

I've got at least 3 'spare' Renix clusters, but all of them have issues, near as I remember I don't have any HO ones sitting around.  They're easy to find though.  So I should be able to pick one up and piece this together at some point.

 

The fuel gauge is the kicker because it mounts totally different and is reversed between the Renix and HO.  The Renix fuel gauge resistance range is officially 0-88ohms (empty to full).  Measuring mine it is much more like 0-99ohms (it does show being beyond the F mark when full), which conveniently corresponds with the old standard GM senders and gauges, so there's about a million aftermarket gauges that will probably work fairly well with the Renix sender.  Worst case they'll show not quite full.