Ih8electrical: DRL relay drama

[Shipwreck]

I am wiring a new set of offroad lights that also have a daytime running light and turn indicator function that operates independently of the offroad lights. I want the DRLs to come on automatically once the truck is running. I figured I could do this by wiring a standard 4-pin 40A relay triggered by the "charge" circuit via this thread: https://forum.ih8mud.com/threads/whats-a-good-12v-switched-source-underhood.881174/
I am having a problem when I hook up the relay, the voltage from the "charge fuse" wire drops from 13.4v down to 5 volts. The relay does not complete the connection from pin 30 to 87 and therefore won't send a signal to the DRLs. In addition, the low voltage signal to the alternator regulator causes the charge warning light to come on.
Here is how I have things wired:

I have used the "charge fuse" circuit to power relays in the past for many years. The only difference this time is that I did not add a switch to actvate the relay on demand.

There is also a weird addendum: If I have a weak ground at pin 85, I can activate the relay sending power to the DRLs. Specifically, if I just lightly touch the ground wire to a ground source on the fender, the relay works. Once I make a solid ground, by tightening the wire to a bolt, the relay doesn't work. Either way, once I make that ground connection at pin 85, the charge warning light comes on.
What am I doing wrong?

 

[jonheld]

For whatever reason, the relay coil is loading down that circuit.
I would verify that you have it wired correctly and try a different relay.

 

[Shipwreck]

I've checked my wiring multiple times, replaced an old connection, and tried three different brand new relays. I'm stumped.
Would the gauge of the trigger wire make a difference? Right now, it is the same size as the wire running to the L pin of the regulator. 18 AWG I think. I have a soldered, wrapped connection to the Y-L wire rather than a fuse tap.

 

[thedoughboy]

@landcrshr

 

[george_tlc]

Measure the coil resistance of your relay - that will give an idea of how much current it will draw. I also assume your relay doesn't have a diode across the coil - if you wire that kind of relay 'backwards' you will have issues...

Also, verify that your altgood fuse is good and the contacts to the fuse holder are clean.

I've used that signal for years to operate 2 'automotive' relays and it can happily do that without any issue.

Your ground connection 'weirdness' is also worrying.

Time to get the meter out and measure some stuff to verify good and proper connections.

cheers,
george.

 

[Shipwreck]

Thanks George. I was hoping you'd chime in.
I haven't measured resistance across the relay coil. I don't think these relays have a directional diode, but I'll check.
I'll try to record some data tonight if I can get home from work before it gets dark.

 

[george_tlc]

"saratoga slums" - I assume south bay saratoga? I work in Mountain View, so worst case you could pop over to my work place and I can have a look see...

cheers,
george.

 

[Shipwreck]

Yep. I'm at Saratoga Ave/ Hwy 85. I think I've "cruiser waved" to you or your wife on Lawrence Expressway in the past. Hopefully this won't require personalized expert attention, but I'll keep the offer in mind.

 

[landcrshr]

@landcrshr

I don't exactly know the behavior of the "L" terminal on the alternator.

@george_tlc is it supposed to source current when the alt is working properly?

It obviously sinks current when the alt is failing.

 

[george_tlc]

^ The L terminal should provide nominal +12V while the alternator is running. The warning 'bulb' on the dash has +12V on the other side. So, if the alternator isn't running or broken it will nominally have 0V on the L and the bulb will light up.

If all is 'good' then the bulb has +12V on one side and L provides +12V on the other side so there's essentially 0V across the bulb and it will go out.

In the "olden" days the L was actually providing the initial 'boot' for the field winding to energize when the alternator first would spin up. So, if the bulb was burnt out the alternator would likely not 'power up'. Substituting a LED instead of an incandescent would not be a good thing on the old alternators...

Shipwreck may have an issue with his alternator L signal. If it is not there or the fuse is blown, the bulb will not light up when key is ON (before starting engine). Possibly his bulb is actually trying to provide +12V to the relay coil and thus he is seeing only 5V or so due to the bulb's voltage drop. A bit of debugging should find what is going wrong.

cheers,
george.

 

[Shipwreck]

I found some time tonight to document what I'm seeing.
Here's a picture storyline:
Full charged battery:

Here is the trigger wire connection to the wire leading to the "L" pin at the alternator. it is just below the 7.5A charge fuse. The fuse itself and the contacts are good:

The trigger wire leads to a waterproof fuse box the holds my relays. This trigger wire, the 12v+, and ground wire splits within the fuse box to feed several of these relay plugs. I have pre-wired the plugs to make it easy to add a new relay. I confirmed the wiring; 12v+ to pin 30, trigger to pin 86, and ground to pin 85. Output is pin 87.

I checked resistance across the relay coils. Lowest was 65.5, highest was 80 Ohms. All had continuity from pin 30 to 87 once the coil was activated.

 

[Shipwreck]

Once I confirmed good relays and battery charge I proceded to check voltage of the wiring. No voltage at "charge" fuse with the ignition off:

Once I start the truck, and without the relay installed I get 14v at the charge fuse:

I also don't have an illuminated charge light on the dash:

Once I plug in the relay the voltage drops to ~5V:

And the charge warning lights up on the dash:

 

[Shipwreck]

However, charging voltage at the battery remains the same:

The one breakthrough I had tonight was that I was able to power the relay and light up the DRLs. I'm not sure what the difference from the other day was, but testing two different ground points the relay worked:

And the turn signal function works as well:

But the "L" signal wire at the charge fuse still has ~5V and the charge light on the dash is still illuminated.

 

[Shipwreck]

Since the alternator works fine without the DRL relay plugged in, and the offroad lights work with a switched relay triggered by the same trigger input, I'm pretty convinced this is a grounding issue that is specific to these LED lights.

 

[george_tlc]

Some good measuring going on. The ~ 5V is very suspicious, that is the voltage I would expect if the dash bulb is actually providing the 12V path to the relay coil. The bulb only gets 12V on its other end when ignition key is on or engine is running.

That would imply your L signal from the alternator is bad/disconnected/etc.

A test: if you remove the L fuse, but have your DRL relay plugged in, do you see the same ~5V with ignition on/engine running? And the dash light will be somewhat lit up? With the fuse still removed, measure the voltage on the alternator side of the L connection.

Also, you may not want to run more than a couple of relay coils from that L signal. There isn't a spec of what it is actually capable of providing (current drive).

cheers,
george.

 

[Shipwreck]

If the L signal from the alternator is bad/disconnected, wouldn't that show up as a charging error all the time, not just when the relay is plugged in?

The other day I tried to remove the IG/L/S wiring plug from the back of the alternator to measure continuity and voltage. I spent 30 minutes trying to get the tab compressed and the damned plug to release. I never got it. I'll have to give it another go. I'll make the measurements you suggest at the fuse and report back.

Prior to installing this DRL relay I have one other relay that sends power to the offroad lights. That relay gets its trigger from the same charge circuit, but runs to a dash switch first. I haven't seen this voltage drop when that relay is operating. I installed that relay and switch almost 20y ago.

 

[george_tlc]

No - without the L connected, the bulb would not have voltage on its downstream side and would not light up.

That's why when you first turn the key to 'on' the alt dash light should light up as a 'self test' of the bulb and fuse - since L will be actively low (near 0V potential). The rest of the time if the fuse is blown or there's no L signal the dash light will happily remain off making everything look 'good'.

You're saying the other relay gets nice +12V from the L signal if the DRL relay is not plugged in?

If you remove the 7.5A fuse, you should be able to measure the Alt L signal directly and verify it is +12V with engine running/alternator spinning. You could then run a flying lead from that side of the fuse (carefully, since there's no fuse in place anymore) to the DRL pin 86. Connect 85 (other side of the coil) directly to the battery negative post. Measure across 85/86 and there should be a healthy 12V with alternator spinning.

cheers,
george.

 

[Shipwreck]

Thanks for details George. This is really helpful!

 

[Shipwreck]

You're saying the other relay gets nice +12V from the L signal if the DRL relay is not plugged in?

Yes, the other relay gets +12v and the offroad lights function normally. A switch in the cab completes the circuit to power the coil.
Offroad light relay location:

+14v at the charge fuse with the offroad light relay plugged in:

The offroad lights fire up once the dash switch is flipped. The charge light on the dash doesn't illuminate. All good and normal:

But once the DRL relay is plugged in, the trigger wire voltage drops, and the charge light comes on. Back to it's old shenanigans. The offroad lights remain lit:

Having fun yet?

 

[george_tlc]

Draw a schematic of how the spotlights are wired to the relay and the in-cab switch along with the DRL relay.

What happens if you swap the spotlight relay into the DRL relay spot? Still only ~5V and dash alt bulb lights up?

Where do the DRL get their ground? Is the DRL relay and the spotlight ground coming from the same place?

Somewhere there's some wiring issue going on or some missing info...

cheers,
george.