Hi all --

I have a 93' 4.9L 5-speed XL without a tach. I purchased a cluster from a 93' Lightening on ebay that has a tach and a 120MPH speedo. Everything works except the voltmeter, and of course, the alternator isn't charging.

Here's what I need to know:

Can I change the odometer from my original 85MPH speedo to the new 120MPH speedo. The new odometer shows 98k, and my truck only has 49k on it. If I change it, will the speedometer read correctly?

What are the options on making the voltmeter work and the alternator charge? I've purchased wiring diagrams for both the 93' lightening, and the 93' XL, but they show the pinouts on the cluster are the same. I can tell by looking that the + for the voltmeter on the new cluster is in a different place, but I don't know which pins to swap to make it work.

I have searched the forums, but haven't been able to find anything on changing pins to make this work. I've also searched the Internet, and couldn't find anything either. If anyone knows, please help!

Thanks!

 

Yep, the pinouts are the same.

You have a voltmeter, which measures voltage. You also have a "alt" light that measures current. It also has a resistor in parallel with it.

The bulb, and/or the resistor, burned out. Or, wires going to and from the cluster connected to bulb/resistor, aren't making good contact.

 

Are you saying that Ford designed the charging system on my truck to be dependant on a light bulb completing the circuit? That sounds pretty crazy, but I'll check it just to be sure.

But if that's the case, then why does the + on the new clusters voltmeter go to a different pin on the plug?

Thanks

 

I checked the bulbs, and resistors. All are ok. Any more ideas?

 

Yes. It's been that way since 1969. Cars got rid of that "feature" before the pickups did, which was just before the body style changed to the new superduty and "rounded" F150 came out.

That's why there is a resistor in parallel with the bulb. So if the bulb burns out, the circuit is still complete and the alternator (well, the regulator actually) still does something useful.

[quoteBut if that's the case, then why does the + on the new clusters voltmeter go to a different pin on the plug? [/quote]

Not sure what you're refering to, my 92-96 diagrams indicate the clusters are the same. I happen to know that the 95/96 clusters are different because of the ODB-II stuff.

Thanks[/QUOTE]

 

Yep, you're right. I spent some time reading about it today, but I still have a hard time believing they would do something like that. Anyway, that's another episode...

It looks like (+) trace to the voltmeter winds up on different pins on the two clusters. However, I could be seeing things....

Any other things to check??

Also, I think the speedo is probably wrong on the new cluster. It seems like I'm going slower than it's reading. Would changing the board on the speedo fix that?

Thanks!

 

I guess I was a little pre-mature on the "not charging" diagnosis. I assumed that since the volt meter wasn't working, I had the same problem I'd read about in other posts. That wasn't the case.

For some reason, the ground to the voltmeter wasn't grounded. So, I soldered a wire from the ground on the fuel gauge to the ground on the voltmeter. Problem solved. Here's a pic --



Thanks for your help!

 

The speedo's are programmable. You can change the divisior using the reset and select buttons, to change the ratio at which it converts pulses from the ABS system (speed) to what it displays. More than likely that cluster was in a truck that had larger diameter tires than your truck has.

here is how to do it:
https://www.ford-trucks.com/article/...ND_BRONCO.html

 

I have a 95 F150. I tried putting a cluster from a 93 diesel in my truck so that I would have a tach. I had the same problem w/the voltmeter. The alternator wouldn't charge the battery untill I put the old cluster back in. Also, the tach was barely moving. I couldn't get the diesel tach to real over 1k rpms.

 

I fell for the diesel cluster thing the first time too. I never did figure it out, so it went on ebay. I'm pretty sure the tach on a diesel gets the signal from the injector pump (or somewhere), since there isn't a coil. However, the voltmeter worked on mine.

I did recalibrate the speedo, but I still don't think it's right. I used the chart for the conversion constant, and I don't think it's perfect. I'm planning on taking some measurements of the tires and trying again. I've got 5 more chances with this PSOM --Maybe I can get it right!

Another thing I'm not sure about is changing to the 120MPH speedo. It may just be me, but it almost looks like the needle is where it would be on the 85MPH speedo. i.e. 45MPH is straight up on the 85 speedo. On the 120, when it seems like I'm going 45, it's reading around 60 -- which is where the needle would point at 45 if the 85MPH face was on it.

 

The diesel cluster gets its signal from a switch that opens and closes with the RPM's, shorting the input to ground, opening it, and repeating endlessly. I believe it's a magnetic hall effect switch.

We had a lot of confusion about the diesel cluster working or not working in gas trucks... and while I was part of the group that suggested it does work, I too am confused.

Why? Because until i went digital, I had installed a diesel tach cluster into my 351W powered F350 crewcab, and without any other changes, it worked absolutely fine.

So, who knows!

Regarding the 85 or 120mph speedo, the "arc" is the same, about 270 degrees from 0 to max speed. The PSOM module is supposed to move the needle to match the scale, and the pulses per mile is the same regardless of the cluster. The intelligence is in the cluster. The RABS system provides the same pulses per mile.

According to the Ford Service Manual...

 

I just checked (with a multimeter) my "bad" cluster, and there is 510 Ohms between the pins that the "AMP" bulb (and resistor) are connected across.

I guess that's the next thing I need to check ... where the VOLT and AMP connector pins are on my original cluster compared to the "bad" one.

 

I pulled my original cluster out again, and found where the "AMP" light (and resistor) are connected. It's a completely different place to the cluster I had tried to "upgrade" to - actually on the other connector. I traced the equivalent pins on the "new" cluster and found that one ends up at the mysteriously labelled "FUEL RESET" pad that doesn't appear to have any purpose, and the other runs all the way across to the piece of the circuit "board" that sticks out to the side, as if for a diagnostic hookup or something. It may be time to pull out the soldering iron.....