Si Click

Si Click

Well-Known Member
This evening my son installed some LED replacement headlights on his 1999 D90 TD5.
All was well, car drove fine, until while adjusting the alignment, everything went dark. No power, no engine start, nothing. To quote his text "Nothing happens when the key goes in the ignition. Odometer still reads, but otherwise as if the battery were disconnected."
Any ideas why this suddenly happened? Could LED headlights overload the system?
To check the fusible links I'll need to remove his aftermarket seats which is a right PITA. Is there anything else obvious I should be looking at?
 
Si Click said:
This evening my son installed some LED replacement headlights on his 1999 D90 TD5.
All was well, car drove fine, until while adjusting the alignment, everything went dark. No power, no engine start, nothing. To quote his text "Nothing happens when the key goes in the ignition. Odometer still reads, but otherwise as if the battery were disconnected."
Any ideas why this suddenly happened? Could LED headlights overload the system?
To check the fusible links I'll need to remove his aftermarket seats which is a right PITA. Is there anything else obvious I should be looking at?
Click to expand...
Have you checked the main fuses in the engine compartment, sounds like they would be suspect? Did you disconnect the battery when fitting the lights? may have left a connector loose?
 
Maybe the voltage dropped below threshold because of the testing and alignment of the lights with the engine off
I guess check condition of battery first
 
Battery is reading 11.8v, so a little low but not too bad.
The lights and truck were working fine after installation. I don't know if he disconnected the battery or not, but as they were all working fine afterwards a short at the time seems unlikely.
By main fuses in the engine compartment I assume you mean the ones under the driver's seat. No not yet, those are the fusible links I am hoping to avoid having to look at as it will take me at least an hour to get the seat
WhatsApp Image 2018-11-14 at 09.38.34.jpeg
out and about twice that to put it back.
 
Odd.
I pressed the inertia switch in the engine compartment - nothing.
I pulled all of the passenger compartment fuses (which were all fine), I also unplugged and replaced the yellow SM relay.
After fixing nothing the power came back.
Dodgy fusebox perhaps, or could the relay have been the issue? o_O
Changing both would seem sensible. Thanks for the suggestions guys.
 
Very hard to troubleshoot electrics with a knackered battery confusing things. I’d say 11.8V with no load is dead flat. What does the battery voltage do when you switch on? Is the alternator charging?

What exactly was done - was it plug and play lights, or was some rewiring involved? Any other jobs done at the same time?

“After fixing nothing the power came back” - usually an intermittent fault like a loose connection or the time spent fiddling with the fuses allowed the battery to recover.
 
As above 11.8v is dead, my 300 has a main fuse box in the engine compartment with the big stuff in it (60A and 30A fuse links) which are the main supplies, however I suspect a flat battery is the main issue
 
The battery is less than 6 months old and is a 100AH unit. The alternator was replaced at the same time and is giving 14+V when running,
I took the battery voltage from the display my son has wired to his dash, Hawkeye is now showing 12.4V and the engine starts happily.
I don't think this is a dead battery issue. This was a digital event - no power then suddenly loads of power.
What seemed to make a difference was disturbing the Starter relay.
 
Si Click said:
The battery is less than 6 months old and is a 100AH unit. The alternator was replaced at the same time and is giving 14+V when running,
I took the battery voltage from the display my son has wired to his dash, Hawkeye is now showing 12.4V and the engine starts happily.
I don't think this is a dead battery issue. This was a digital event - no power then suddenly loads of power.
What seemed to make a difference was disturbing the Starter relay.
Click to expand...
Irrespective of age or capacity if your 11.8v was an accurate battery voltage reading that indicates that the battery was flat at that time. Unless you had the lights on for a long time while adjusting them then its worth keeping an eye on it as you may have something draining it.
 
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