I have been reading the threads on adding a relay in the signal wire from the switch to the voltage regulator in order to supply a good voltage source to the regulator. Is this just an issue with the non IC trucks? As I dig into this on my 91.5 I find that the pigtail to the firewall location of the VR that both the blue signal wire and the green wire come from the alternator. Will adding a relay help a 91.5 and up truck.

Thanks Folks.

 

If your truck has the external VR on the firewall, and gets it's power from the ignition switch then yes. It is a good idea. I burned up a battery with overcharging because of the voltage drop between the ignition switch and the VR. In order to get 14 volts to the VR the alternator had to put 18 volts to the battery. Not good. The relay supplies battery voltage directly when the key is on to energize the relay.

If your truck has the VR as part of the PCM then I can't say about those.

Edwin

 

So what is the wiring route of the signal from the ignition switch? Does it go to the alternator first and then to the VR because when I trace that blue signal wire it goes to the pigtail at the alternator.

 

Referring to the wiring diagram for my 89 the Dark Blue wire comes from a Junction labeled J2 which comes from the ignition switch and feeds a bunch of other circuits and powers the VR. The VR does it's magic then it energizes the field of the alternator. There may be a fuse in the line before the ignition. You can purchase an FSM from Geno's on PDF for about $40 or less. J2 is from the Start/Run position of the ignition switch.

 

Might help. Chronicles of my journey. I did add a ground loop and I believe that helped a lot. Also the headlight relays.

https://www.dieseltruckresource.com/...thread-319711/

Thank you,
BlueW250

 

Thanks. I have had my headlights on relays for may years to reduce the voltage flowing though the switch. I am getting low voltage (about 11v) for a while. I put in another VR and everything is good but then the VR gets fried. I just paid $100 for a Mopar VR and I don't want to fry this one. Will the relay help save them?

 

Yes.

Thank you,
BlueW250

 

Great. Thanks.

 

Just an idea, my 91.5 kept eating VRs, I just purchased an internal regulator kit for around $25 (they are on eBay and some online stores). It was a really easy install and there are how to videos on YouTube. Since then it has been reliable and a steady charge at idle - no more pulsing headlights at idle.