Replaced the alternator with a brand new one, didn't change, still shaky. Going to do the external regulator next.

 

What goes wrong with the ignition switch to cause this? My 91 volt gauge bounces all over until it receives rpm's then smoothes out. I have run grounds to everything but that didn't solve anything.

 

I think it is the PCU at this point. If it does the same thing after I bypass the PCM then I will change my story.

 

I think it is the PCU at this point. If it does the same thing after I bypass the PCM then I will change my story.

 

How could the innition switch possably be bad? It's only 24 years old!!

 

Changed it twice!

 

89-91 with the external regulator, power went through the ignition switch. With time the contacts would wear and become resistive and drop voltage to the regulator. However, any drop in voltage anywhere along the feed will cause a problem. The regulator sees this as a low alternator output and tries to correct it.
On 92-93, they move the power off the ignition switch to the auto shut down relay. The same idea still applies, "However, any drop in voltage anywhere along the feed will cause a problem".

So the problem is not on the ground side, but the hot side.

 

Simple solution: Install a relay to supply power to the fielding circuit and regulator, driven by the run contact on the ignition switch.

 

This is the fix.I had the same problems with the voltage bouncing at idle and even driving down the road.It would blow my headlights.I noticed a voltage drop from battery voltage to reg input voltage.I wired in a relay powered off the battery and used that for my reg input and no more bouncing voltage gauge.

Regulator input must be the same as the battery voltage when using the external reg.

 

I'm with cougar,,,,been there done that,,,,,no wait,,i'm still there,,,have grounded,regrounded,up graded grounds ,,,still ,,there,,have to go thru all the hot stuff next.


whosdunit.

 

This makes me insane. I get the same results with the PCM or an external regulator, so it is obviously a hot somewhere acting up, but I have yet to find it.

I know the relay thing will fix the band-aid, but if I can find the source I can continue to use the PCM regulator (unless the PCM IS the culprit). Second PCM I have tried with the same results though. Could just be an inherent weak point in the PCM, I don't know.

 

Naw, they are pretty reliable. I suspect you have a problem with a connection or switch (relay) somewhere.

I started to compose a lengthy help text when I realized you actually haven't told us what is happening, other than things are blinking and you are going nuts.

Is it going over-voltage and burning out lights?
Is the voltage going low, ie lights dimming?
What was the PCM code thrown?

It ain't rocket science, but nobody here (I don't think anyway) is clairvoyant.

With some detailed information, actual observation sans feelings, I might be able to propose a diagnostic path to the solution.

 

The PCM is throwing this code: 12, 33, 46
12 is normal
33 is because I bypassed the PCM for the A/C
46 is low voltage???
I haven't connected the fluke meter yet, but what I thought was over voltage is being reported as low voltage.

Annoying.

 

I'm starting to think I have a fusible link that is partially gone. I replaced the main wire with a 50 AMP fuse, but maybe it is another one. They all look good though, no blistering or anything.
I hate electrical gremlins.

 

What's annoying is that you have a very nice meter and you won't use it.