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240 Speedometer/Odometer Problems

Beau

New member
Joined
Apr 29, 2018
Foremost, thanks in advance for responding to my thread.

How do I bypass the circutry within the instrument cluster and get the alternator to self excite? Do I simply connect a wire from the battery terminal to the alternator?


Thank you for any help you can offer. I appreciate your time and consideration immensely.
 
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I've been looking at Speedhut and installing a gauge kit with a GPS speedometer. How do I go about bypassing the signal the original speedometer/odometer is sending to communicate with the alternator to initiate a charge to the battery?

I've contacted some specialty shops to see if they could help but there has been no luck. I've also contacted some computer repair shops but they won't/can't repair motherboards.
 
Oops, 3 minutes too late to quote your original post. I'll do this from memory.

First off, the speedo/odo is pretty much a separate unit from the rest of the console. Speedo/odo problems have nothing to do with alternator not charging. If your alternator all of a sudden isn't charging, and you haven't been messing around with anything in the dash, then try spinning the fuse first -- fuse 13 IIRC, but check your owner's manual.

To get an alternator to charge, all you need is a wimpy little dashboard lamp between the alternator wire and +12v. This wimpy little lamp provides just enough current to energize the alternator field windings so that they can generate power.

Second of all, a '93 dashboard gauge cluster is not a rare part. Just post in Wanted, with a picture of your original failing unit, and ask for a replacement.

You can also swap the speedo/odo assembly between clusters -- remove the screws in the outer ~1/2" from the back side of the cluster. This should free up the main board. Now carefully remove the 4 screws from the center of the speedo. This should free up the speedo/odo. Be careful that you don't drop the speedo/odo once unscrewed.
 
I've replaced the speedometer already with another from a 91' and it was incompatible. It allows the car to run and the alternator to charge but it does not engage the odometer or speedometer. The motherboard on the original speedometer had a four prong/four channel connection with the instrument cluster. The one I purchased used has a three channel connection. Works, but not properly. At least now it is charging. Are you saying that the wire that leads from the battery to the "dummy light" to the alternator does not go though the circutry of the speedometer?
I want to bypass the "dummy light" and excite the alternator externally (under the hood, not the dash) how would I go about doing that properly?

I mistakenly fried the circutry in the mother board of the speedometer when I was replacing the 25t gear. In a rush I connected, what I believe was the tachometer cable, to a post that it should have never been on.

The alternator stopped working immediately after the circutry on the motherboard of the speedometer fried

When I replaced the speedometer the alternator started working again.
 
But the speedo has 0 to do with the alternator. The alternator light has everything to do with the alternator. If that bulb is not working, the alternator will not excite. Fuse, bulb, and wiring to and from light to alternator. That's all that matters. Alternator needs 12v switched to excite.
 
Okay, understood. Thank you for clarifying. Now, how do I fabricate a new connection from the fuse to light to wiring to alternator without a light? Is there something that you can use in place of a bulb? Could I thoeretically run the wiring from the fuse through a "bulb" to the alternator? I do not want a battery/alternator light on my new dash setup.
 
Even if you gut everything else, I'd still keep a lamp so that you know when the alternator or battery fails. If you're set on removing all of it, try a 43ohm 2Watt resistor -- if it heats up too much before starting, try a 50ohm 2W.
 
Which wire is responsible for activating the battery/alternator light? When installing the resistor which wire do I reconnect?
 
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