How to Convert Instrument Cluster Lights to LEDs with Factory Blue-Green Tint

I have just completed converting my 1983 308 QV’s instrument cluster to LED bulbs. With the LEDs, my instrument cluster looks GREAT! Below is a diagram of the 1983 308 QV instrument cluster.

I had three requirements that may be a bit different than other people’s:

1. Conserve the original blue-green color of the lighting as it came from the factory.
2. Ensure each gauge is uniformly lit and that all gauges are at the same brightness.
3. Brighten the instrument cluster sufficiently to see the gauges but not make them overly bright.​

I was successful in achieving these three goals, but it took some trial-and-error.

Some notes:

1. The 308 does not need bright bulbs in some places. Everyone selling LEDs is making them as bright as possible. Nobody’s advertising pitch is “Our bulbs are dim!”.

2. Almost all LED bulbs are “cool white” (6000k in color). The factory incandescent bulbs are “warm” in color. There are “warm white” LED bulbs (3000k in color), but they are hard to find and some socket types are unavailable (at least I couldn’t find them).

3. There doesn’t seem to be a standard description of LED bulb dimensions.

4. The 308’s instrument cluster has 3 different styles of bulb sockets; one standard BA9s base but two different T5 wedge sockets. With incandescent bulbs, the different T5 sockets don’t matter but with LEDs they do. Only certain LED bulbs work.

There are already many threads on instrument cluster LED conversions and I used those as a basis to get me started. Do a search. There is some great help already documented. The problem is that the LEDs available for purchase seem to be constantly changing.

Here is what I did:

Bypassed rheostat - Bypassed rheostat (because LEDs do not respond to voltage changes) by crimping appropriate connectors onto both ends of a short jumper wire.

Converted BA9s base indicator bulbs to LED - Replaced five indicator bulbs with LED equivalents (Low Fuel, Low Oil Pressure, Brake Failure, High Beam Indicator, Parking Brake Warning). I used these 120 lm “warm white” bulbs: https://www.amazon.com/dp/B09YPYHCG8

Converted T5/74 base indicator bulbs to LED - Replaced six indicator bulbs with LED equivalents (4-Way Flasher, Left & Right Turn Signals, Parking Lights On, Seat Belt Reminder, Low Engine Temperature). All used 120 lm T5/74 base cool white LED bulbs (I couldn’t find warm white with this socket style). Parking light bulb was too bright (it is on anytime the headlight buckets are up) so blacked out top of bulb with black paint to dim it down. I used these bulbs: https://www.amazon.com/dp/B06XY3NT9N

Did NOT convert two indicator bulbs - “Interior Fan” and “Alternator Failure” T5/74 bulbs were left as incandescent bulbs because they cannot tolerate LEDs.

Converted small gauge illumination bulbs to LED - All small gauges (including oil temp and clock) used the 120 lm “warm white” BA9s bulbs: https://www.amazon.com/dp/B09YPYHCG8

Converted speedometer illumination bulbs to LED - Used two 230 lm T5/74 base “warm white” LED bulbs. Blacked out top LED with black paint to reduced two bright spots on speedo gauge. The bulbs I used were: https://www.amazon.com/dp/B09SYQB763

Converted tachometer illumination bulbs to LED - Tach needs very bright lights. I used two 490 lm (forward) / 340 lm (two sides) BA9s “cool white” bulbs tinted slightly with green acrylic varnish to balance color with the warm white bulbs used elsewhere. Adjusted angle of bulbs to even-out brightness across gauge. I used these bulbs: https://www.amazon.com/dp/B09LST3J6L
I used this green acrylic varnish (a model-building buddy lent me some): https://www.amazon.com/TAMX25-81525-Acrylic-Clear-Green/dp/B0099WPKM8
He did not have yellow clear and that might have worked equally well. You have to wash on a very light coat (dilute the varnish with solvent). Too much and the gauge gets too green and too dim.

I bought a couple more types of bulbs than what are listed above. As I already mentioned, a problem is that LED marketing competition drives bulb manufacturers toward making the LED bulb as bright as possible. We don’t necessarily want this. At first, my tachometer was too dim and my speedometer was far too bright. I used a light meter app on my iPhone (Light Meter LM-3000) to measure the relative brightness of the bulbs to figure out how to select more appropriate bulbs. The brightness specs listed on Amazon are helpful but inexact.

A few random notes:

• All bulb sockets are friction fit into the instruments: you just pull them to remove. Unfortunately, you need to remove the instrument cluster to get to most of them.

• The BA9s bulb twist out of their socket and the base 74 bulbs just pull straight out.

• Test the bulbs after inserting into their sockets but before installing the instrument cluster. The T5/74 base bulbs may need to be flipped over for them to light.

• There doesn’t seem to be any standard size to the bulbs themselves (only the bases). The maximum diameter of the BA9s bulbs can be 11.3 mm. The T5/ 74 bulbs are quite small so I didn’t measure.

• The T5 base is also used for 12v landscape lighting which can be extremely bright. Shop carefully.

• Look for bulbs that have at least a 270 degree light distribution.

• “Cool white” bulbs are much more readily available than “warm white” so, if you don’t mind the instruments being slightly bluer, that is an easier way to go than what I did. And, color temperature doesn’t have to be exact.

I hope this helps.

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Ha! Nope! That sounds like work, which is something I try to avoid.

I do enjoy tinkering on my car and figuring stuff out like this. Actually, I enjoy doing the write-ups too. For me, it's a bit like reliving the project except with all the frustrations rewritten as triumphs. My Magnus Opus was my expansion tank cap thread (answer: buy a Stant 10230).

The reality is that the bulbs are very easy to buy. The hardest part of the project is getting the darned instrument cluster out of the binnacle and then unplugging and labeling the multitude of connectors. I can't help with that. Once that is done, popping in bulbs is easy. The only requirement for electrical competency is testing each bulb before putting the cluster back in which I can't help with either.

I did the LED project in conjunction with a couple others. My tachometer case had cracked and was rotating freely so I glued that back together. I also installed TacElf's oil pressure sensor modernization kit which required that a voltage regulator be installed at the back of the oil pressure gauge (it is SO COOL to actually see the true calibrated oil pressure... heck, it's cool just to see the needle move now).

 

I did not and I confirmed that it is not harmful to the system to use the existing flasher with the LED indicator bulb. (Note that the only LED bulb currently in my flasher system is the indicator bulb in the instrument panel.)

 

Thanks for the kudos.

The Amazon write-up for that bulb has horrible inconsistencies. It says 10-30v in one place and 12-24v in another, it lists warm and cool color temperatures in different places too. Ultimately, they ARE warm white 12v bulbs. They were $14.99 when I bought them and sold in a pack of 8.

It may well be that the other “12v” pack of 10 currently for $16.99 is the same bulb, but I am only speculating.

To be perfectly clear, I ordered ASIN (Amazon Standard Identification Number) = B09YPYHCG8. You can search the ASIN in Amazon and get the exact product.

 

The green varnish would also be a good way to tint a plain LED bulb to replace the bulb goes under the handbrake lever that illuminates the console switches on a 308.

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