speedo gauge cluster issue - any thoughts???

[Jbwalsh76]

In full disclosure...I'm a newbie...I just bought my first EB (had it about a week now).

My speedometer and ALT aren't reading at all (which I knew about before buying) and my other gauges (ie temp, oil and fuel) are pegged all the way as soon as I start the engine. Engine is running fine...

Anybody ever have this happen before?

I first thought gauge was toast, but now I'm thinking maybe just an electrical short.

Any help would be greatly appreciated.

 

[Millercorey]

Have you checked the lines in the back to confirm they’re present and attached? The speedo isn’t electrical in any way to my knowledge - it spins. Either not there or not attached is my guess.

 

[DirtDonk]

Hey JB, welcome. Ok, so you've been here for a month and have 10 posts, but I figured I'd say hey anyway.

These things are all un-related for the most part, even though they share the same cluster. So a few details please.
For example, is this stock wiring? Original and in good shape, or totally hacked by the previous owners (the dreaded "PO's" that you read so much about with Broncos), or perhaps replaced with new.

What year Bronco? Basically, what shape is it in?

The ammeter is it's own gauge. Nothing else connected, but let us know if it might say "volts" on it which would mean it's been replaced.
The fuel and temp and press are all on the same circuit so the pegged gauges may be a failed IVR (instrument voltage regulator) or bad sending units. Though all three being bad the same way is unlikely.

The speedo could be the cable, the gear, or the gauge. Easy test is to go under the truck and follow the cable back to the side of the transfer case. Loosen the bolt and pull the assembly out and check the condition of the gear. If it's in good shape spin the gear by hand and feel if it's smooth and easy.
If it is, do it again and watch the speedometer to see if it's moving.

Anyway, more to come, but let us know the basic layout.

Thanks

Paul

 

[Broncobowsher]

The 3 gauges that all peg. That is a classic bad IVR (insterment voltage regulator). Either it has a bad ground that will cause the exact issue, or the points inside are fused together.

The amp meter may have been bypassed. Do you have an upgraded alternator? Modified wiring? Aftermarket wring harness?

Speedometer is 100% mechanical. typically pull the speedometer cable out of the transfer case and make sure all the teeth are on both gears. Try spinning the cable with a drill as you watch the speedometer. Works? (and the gears are not stripped out) the gear on the output shaft is probably spinning. Not work with the drill? At this point you have a bad cable or a bad speedometer head. Disconnect the cable at the back of the speedometer and check that it spins with the drill.

Further hint, if the odometer works but the speedometer doesn't, you know the cable up to the head is good since the odometer is moving. That is a bad speedometer head.

 

[Jbwalsh76]

Thanks guys. I plan to dig into this tomorrow to see if the cables are connected properly or even there at all.

My EB is a '77...it's in good shape. Alternator was upgraded, so that might explain the amp meter. IVR/bad ground seems to make a lot of sense.

Granted this one is new to me, but the previous owner doesn't appear to have cut corners. I'll know more tomorrow.

Thanks again for the feedback.

JB

 

[DirtDonk]

If anything is in doubt as to how or what was used to update one system or another, definitely post up pics of it under the hood. Or just in general too, since we love pics of new Broncos!

You can use your "garage" and "gallery" functions, but to upload directly to the discussion you will need to become a contributor for 12 bucks a year. Totally worth it if you're going to keep busy here and want to post up a lot of higher resolution pictures.

Do you know what alternator was used? If it's wired directly to the battery it's because it's likely a higher output unit such as a Ford 3G (original was a small case 1G between 43 and 55 amps) or a GM/Delco unit and the original Black w/yellow charge wire that runs through the ammeter's inductive loop is considered too small for anything over 70a to give some leeway.
Aftermarket harnesses, such as the Centech, can handle more, but should still be limited to 100a or less, where a common 3G would be rated at 130a or more. There are 95a versions too, but the most common swap is to the 130.

A workaround is to change the amp gauge out for a volt gauge in the same place (https://www.wildhorses4x4.com/product/Voltage-Gauge-Stock-Cluster/dashgauges) so you can still keep tabs on what's going on with the electrical system.

Paul