Resistor bypass and belt squeal **FIXED**

[Finnegan1008]

I apologize if this has already been covered and I'm beating a dead horse. If there is already good info on this please direct me to it.

My truck came to me with the resistor bypass already done.

When ever I turn on my headlights I get belt squeal. It's still happening despite tightening up the belt. This raises a few questions:

• Does doing the bypass over load the driver side alternator and forward battery? As far as I know this is the same headlight circuit that is used on a 12 volt / single alternator truck. I think the resistor by pass essentially mimics this?
• Is this a product of 1986 wiring that is creating a too much resistance?
• Could this be a problem with the aftermarket alternator that came on the truck?

 

[WWRD99]

I apologize if this has already been covered and I'm beating a dead horse. If there is already good info on this please direct me to it.

My truck came to me with the resistor bypass already done.

When ever I turn on my headlights I get belt squeal. It's still happening despite tightening up the belt. This raises a few questions:

• Does doing the bypass over load the driver side alternator and forward battery? As far as I know this is the same headlight circuit that is used on a 12 volt / single alternator truck. I think the resistor by pass essentially mimics this?
• Is this a product of 1986 wiring that is creating a too much resistance?
• Could this be a problem with the aftermarket alternator that came on the truck?

The resistor bypass does put the load on one battery vs 2...goes directly to 12 volt vs being knocked down from both batteries 24 volt to 12...my guess would be the battery is weak and the headlights load is bringing it down. Put a volt meter on the block and see how low the volts go. Are the batteries group 31s? Also are you running the stock halogen bulbs still? Are both the same brightness like one is dimmer than the other? Could have a bad ground on one or the bulb going out.

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[Finnegan1008]

Thank you for the reply,

yes they are both group 31 batteries purchased in 2022. They tested fine when I got the truck about 4 months ago. I will re test to confirm.

what do you mean by putting a volt meter on the block? I you saying to check for voltage drop through the headlight circuit?

or go from block to batter negative and check for less than 12 volts?

bulbs are sealed beam halogen and are both bright and totally usable.

I will check for voltage drop and any potential bad grounds.

 

[WWRD99]

Thank you for the reply,

yes they are both group 31 batteries purchased in 2022. They tested fine when I got the truck about 4 months ago. I will re test to confirm.

what do you mean by putting a volt meter on the block? I you saying to check for voltage drop through the headlight circuit?

or go from block to batter negative and check for less than 12 volts?

bulbs are sealed beam halogen and are both bright and totally usable.

I will check for voltage drop and any potential bad grounds.

Good deal on the batteries..the block I should have said where the 12 volt line comes from the battery to the firewall. Pop a heat gun on that too just to see if you have some resistance on the connection. Headlights draw some amps but not a ton. The blower motor on high should pull more...I'd bet if you had the lights on bright and the blower on high you should be able to find where the problem is. I Pop jumper cables to ground on the block sometimes just to make sure that's solid too. Could be that simple...crappy ground on the pass head to body or block or both.

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[Finnegan1008]

Good deal on the batteries..the block I should have said where the 12 volt line comes from the battery to the firewall. Pop a heat gun on that too just to see if you have some resistance on the connection. Headlights draw some amps but not a ton. The blower motor on high should pull more...I'd bet if you had the lights on bright and the blower on high you should be able to find where the problem is. I Pop jumper cables to ground on the block sometimes just to make sure that's solid too. Could be that simple...crappy ground on the pass head to body or block or both.

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This all seems logical I’ll check it out this weekend. Thanks for the advice!

 

[cucvrus]

If it were mine, I would undo the resistor bypass. That is me. I have privately been driving a CUCV since 1995 and never did that bypass. I have owned many. Never needed to and never had cascading glow plugs or burnt wiring. I maintain the trucks I have and fix things as I see them happening. I don't wait till I am cranking it till the relays get stuck fast. Good Luck. I still have the original 13G glow plugs in all the CUCV's under my control. But you are pulling all the juice from the front battery with the bypass. Get the batteries load tested also and have the alternators checked.

 

[DeadParrot]

Unless you know the belts are new and correct, if tightening them didn't help, replace with known good and correct belts.
Check for possible oil/fluid leaks also. Doesn't take much to make a belt slip.

 

[Finnegan1008]

Unless you know the belts are new and correct, if tightening them didn't help, replace with known good and correct belts.
Check for possible oil/fluid leaks also. Doesn't take much to make a belt slip.

they are the gates belts recommended on this site. They are all in the middle of the adjustment range and a couple of months old

 

[Finnegan1008]

If it were mine, I would undo the resistor bypass.

I am considering this, or potentially going 12 volt using one of the methods outlined by Roscommon.

I would like to understand how splitting the system with the bypass loads up the alternators. I need to study up on the effect on amp draw on both alternators by doing this.

I want to bring this truck to like new functionality.

 

[WWRD99]

I am considering this, or potentially going 12 volt using one of the methods outlined by Roscommon.

I would like to understand how splitting the system with the bypass loads up the alternators. I need to study up on the effect on amp draw on both alternators by doing this.

The splitting is actually extremely simple. The resistor gets its power from the fire wall junction box which both batteries are hooked to giving it 24 volts...this is stock. Removing the resistor only requires running the power wire to the glow plug relay from the 12 volt junction box next to the glow plug relay...which I assume how yours is now. I'm not sure why gm did the big resistor part vs just going off the 12 volt from the start other than using both batteries to power the glow plugs could be considered better...not drawing down one battery hard every cold start.

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[Finnegan1008]

The splitting is actually extremely simple. The resistor gets its power from the fire wall junction box which both batteries are hooked to giving it 24 volts...this is stock. Removing the resistor only requires running the power wire to the glow plug relay from the 12 volt junction box next to the glow plug relay...which I assume how yours is now. I'm not sure why gm did the big resistor part vs just going off the 12 volt from the start other than using both batteries to power the glow plugs could be considered better...not drawing down one battery hard every cold start.

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Yes mine is setup as you described. So if I understand correctly, the stock resistor is only getting use when the glow plugs are active?

 

[WWRD99]

I am considering this, or potentially going 12 volt using one of the methods outlined by Roscommon.

I would like to understand how splitting the system with the bypass loads up the alternators. I need to study up on the effect on amp draw on both alternators by doing this.

I want to bring this truck to like new functionality.

As far as the alternators go for the glow plug resistor they don't really have anything to do with how it gets power since the battery/s do all the work. I like the 24 volt system even though all mine don't use the resistor. The starter is about it on the engine. I use the jump port for running power tools and jumping all my other trucks and gensets if they go dead.

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[WWRD99]

Yes mine is setup as you described. So if I understand correctly, the stock resistor is only getting use when the glow plugs are active?

Yes the resistor is only used for direct power from both batteries through the glow plug relay to the glow plugs in the stock setup. Other than that it does nothing. So in theory back to your belt squeeling issue, one battery getting the glow plugs going will definitely load the one alternator more because it is trying to charge that battery back up from the glow plug load plus starting the truck. Hence the belt squeal and high load on that alternator. This leads to 2 directions...wiring up the resistor back to stock so both batteries do the work or 2 make sure the battery and alternator are in perfect condition to handle that load on its own.

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[Finnegan1008]

Yes the resistor is only used for direct power from both batteries through the glow plug relay to the glow plugs in the stock setup. Other than that it does nothing.

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Ok good to know, my glow plugs are on a manual push button and work flawlessly (another mod done by the prior owner).

I will stay on the course you outlined in post #4

 

[WWRD99]

Ok good to know, my glow plugs are on a manual push button and work flawlessly (another mod done by the prior owner).

I will stay on the course you outlined in post #4

Yeah I don't have that on any of mine but I know it works. Make sure you don't run them to long they'll expand and stop working....then that'll be an entirely new thread to fix.

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[Finnegan1008]

Yeah I don't have that on any of mine but I know it works. Make sure you don't run them to long they'll expand and stop working....then that'll be an entirely new thread to fix.

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They did it because the original card crapped out. I’m going to eventually get a new card in there and revers it. There are about 50 other nagging issues that are taking my nickels and dimes in the mean time.

 

[cucvrus]

I am considering this, or potentially going 12 volt using one of the methods outlined by Roscommon.

I would like to understand how splitting the system with the bypass loads up the alternators. I need to study up on the effect on amp draw on both alternators by doing this.

I want to bring this truck to like new functionality.

I have no idea.

 

[WWRD99]

They did it because the original card crapped out. I’m going to eventually get a new card in there and revers it. There are about 50 other nagging issues that are taking my nickels and dimes in the mean time.

Thats not a big deal really in the scope of things! As long as it starts good.

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[Tinstar]

The stock setup works very well and is very reliable when taken care of.
Spend the time and money now and it will payoff several fold later.

Push buttons/card deletes/bypasses/ conversions are fine if that is what the owner chooses, but the stock system does the job very well. It is what it is.

Some guys will spend more time and money bypassing an issue instead of fixing the original issue.

 

[Barrman]

Check the pulley on the driver side alternator. They are stamped steel and can bend out over time. The sides of the belt only should be touching the pulley. If the bottom is touching then the belt can’t work correctly.

I am not entering the resistor/bypass arguments. Just stating I have 3 vehicles running the glow plugs just off a single battery. With that written I never get belt squeal unless the front battery is already low on voltage for whatever reason before I turned on the key. Make sure both batteries are fully charged and load tested before you do anything else. That is why the very first thing in the electrical trouble shooting section of the -20 TM says to do just that first.