99 GMC 3500 wiring issues

Chris Rogers · May 22, 2016

rephrase that - were. they took them off line.

performax may be able to help as well. 07-5482-7833 - ask for kevin. he should be able to kick you in the right direction.

Clinton · May 25, 2016

If anyone can help with my next drama...

The alternator output is only 12.26 volts, same at battery when running. The tacho is still not working and the wait to start light cycles about 4 times before turning off, then I start and its fine. I'm sure its not normal, are the glow plugs cactus or something else??

Chris Rogers · May 25, 2016

Do you have an alt light? Does it show when key on? Does it stay on when the truck is running?

Clinton · May 26, 2016

I'm not sure about an Alt light. I haven't seen one light up. I think the alt has just given up. If it as corroded connections surely id get a different reading from the alternator to the battery, but all readings are the same. strange.

Dahead76 · May 26, 2016

If I'm not mistaken the tach on the 6.5s gets the signal from the alternator. If it's going out then that could be the reason the tach isn't working.

Clinton · May 31, 2016

Hi again,
Thanks for advice. So i found that the white and brown wires for the tacho and exciter were going nowhere, as in not even connected to the alternator. Ive since fixed that and hooked them up directly, but have also since found out that my alternator has been modified, and no longer has an internal regulator. To make matters worse, there is no external regulator. So having hooked up the wires, I now have a battery light (Yay), but it stays on all the time (nooo) and the tacho only works over 1500rpm.

Clinton · May 31, 2016

By the way.. alternator was tested and still performing. It has a huge ground wire, a huge charging wire to battery, a red and a black wire which corresponds to a white/yellow coloured wire and brown wire.

Chris Rogers · May 31, 2016

Sounds like you need to grab the correct alternator for this one.

Good to see you are getting somewhere with it.

Clinton · May 31, 2016

Yeah you may be right. I think it's not far off. With the tach coming on over 1500rpm, I think that the alternator is still not generating, but at those revs the white wire is being charged anyway and therefore giving a response on the tach.

The brown wire is not hooked up right yet. I'm going to bypass it tomorrow and hook up straight to the battery which should turn the alternator on at full power, at least to test it out. As the regulator was removed from inside the alternator, I'm going to have to add one.. that's where im stuck.

Chris Rogers · May 31, 2016

Easier to put the correct one on it. Ext reg would be more of the ambulance gear that's been added given that there would have been extra reserve power added to it when built.

99 GMC 3500 wiring issues

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