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Dj, ASE Certified Technician
Category: Toyota
Satisfied Customers: 1910
Experience:  ASE Master Tech, 30+ years in automotive repair.
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Toyota 4x4 Truck: I have a 1988 Toyota 4x4 truck with a 22RE

Customer Question

I have a 1988 Toyota 4x4 truck with a 22RE engine. The trans oil temp light and the charge light stays on. I removed the alternater and took it to have it tested, it showed that it was no good. I purchased a rebuilt alt at the time, and just for GP I had them test it before I put it back on the tested good. Installed the alt and still same problem system is not charging and the trans temp light is on along with the charge light....any ideas?
Submitted: 2 years ago.
Category: Toyota
Expert:  Dj replied 2 years ago.
Hello and thank you for trusting us with your question. I'm DJ.
The first thing to try is to swap out the 7.5 amp CHARGE fuse. Don't even look at it, just replace it. I've seen them get hairline cracks in the fuse element that you can't see but they won't conduct. So it might look good, but still be bad.
If it's not the fuse, there are three diodes on the back of the instrument cluster, at least one of them is bad.
These are easy to fix if you've got a soldering iron. If you can find a Radio Shack that's still in business, the diodes are $1.50 each. Model: 1N4001 Catalog #:(###) ###-####
If there's no Radio Shack any shop that sells electronic parts will have a 1N4001 diode. It's one of the most common. When you swap them out, just make certain that the band that's painted on the end of the diode points the same way.
A soldering iron is maybe ten bucks, That's still cheap compared to buying a new instrument cluster.
Please let me know if you have any additional questions on this or if there is anything more I can do to help you.
Customer: replied 2 years ago.
Swapped out the such luck. So, my next step is to change out these diodes? And I suspect they are directly inline of completing the charging circuit? In other words i'm asking if these are bad the sytem won't charge? right? and not just a matter of the lights being on
Expert:  Dj replied 2 years ago.
It won't charge if the light is on.
The diodes are on the circuit board that's on the back of the instrument cluster.
Customer: replied 2 years ago.
Sorry it took a couple of days to get back to you. OK, I went to Radio Shack purchased the 1N4001 diodes that you prescribed. Installed the 3 of them and and the system is still not charging ...the lights are still on??? Any more trouble shooting ideas? I've been through all the fuses and put in a new 7.5 in that circuit just because . Nothing seems to point me to a relay, I don't know that there is a charge relay? At this point I don't know what could be causing all this.
Expert:  Dj replied 2 years ago.
I'm surprised that it didn't solve the problem.
Have you got a volt meter? You'll need one to continue testing.
Customer: replied 2 years ago.
Yes I have a voltmeter
Expert:  Dj replied 2 years ago.
With the black lead of the volt meter grounded and the engine running, measure the voltage on both metal nubs on the 7.5 amp CHARGE fuse, the 10 amp ENGINE fuse and the 7.5 amp IGN fuse.
Then measure the voltage on the white wire that comes out of the alternator with the engine revved to about 2000 rpm.
Make certain that the connector is pushed fully into the alternator. They are hard to seat.
Let me know what you find.

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